Owner’s Manual
4-Port USB Serial Adapter
for Windows®
Model: USA-49WG
1111 W. 35th Street, Chicago, IL 60609 USA
Copyright © 2010 Tripp Lite. All rights reserved. All trademarks and registered trademarks are the sole property of their respecꢀve owners.
1
2.1 – Capabiliꢀes
The Keyspan USB 4-Port Serial Adapter provides FOUR male DB9 serial ports which support RS-232 asynchronous
communicaꢀons at data rates up to 230 Kbps.
Keyspan USB 4-Port Serial Adapter Ports
The four DB9 ports on the Keyspan Adapter are seen as COM ports by Windows. The Keyspan COM ports are
interfaced via the “Win32 Communicaꢀons API” and are then available to any program that accesses COM ports via
this API.
By default, the COM port numbers assigned to the Keyspan adapter are the first unassigned (available) COM port
numbers in the Windows registry. For example, if COM1 and COM2 have already been assigned or set aside by any
soſtware or hardware, the Keyspan adapter will take the next available COM port number (COM3).
On Keyspan adapters that have mulꢀple serial ports, the Keyspan soſtware will assign a COM port number to
each serial port on the Keyspan adapter. In the above example, the Keyspan adapter will get COM3 for the
1st serial port, try to assign COM4 to 2nd serial port, etc. It is possible to have an adapter with COM3, COM8,
COM9, and COM10.
The COM port number(s) of your Keyspan serial port(s) can be accessed via your serial device’s soſtware (Palm’s
HotSync Manager, Wacom tablet control panel, etc.).
Note: You can connect more than one Keyspan USB 4_Port Serial Adapter to your USB equipped Windows computer.
The DB9 ports on subsequent adapters will have a different COM port number.
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3.1 – Installaꢀon Instrucꢀons
Installing the USB 4-Port Serial Adapter Soſtware for Windows Operaꢀng Systems
Step 1 – Insert the Keyspan Serial Adapter CD-ROM.
Turn your computer ON. When your computer starts up, place the Keyspan USB 4-Port Serial Adapter CD into the CD-
ROM drive.
Step 2 – Run the Keyspan USB Serial Soſtware for Windows Installer.
If the Keyspan Adapter is connected to your computer, disconnect it now.
Locate the Windows driver and double click on it to begin driver installaꢀon.
Follow the instrucꢀons on-screen to complete the installaꢀon.
Step 3 – Soſtware Installaꢀon Complete!
Now that you have installed the Keyspan USB 4-Port Serial Adapter soſtware, you are ready to install the Keyspan
USB 4-Port Serial Adapter hardware.
Installing the Keyspan USB 4-Port Serial Adapter Hardware
Step 1 – Connect the USB Cable to the Adapter.
If your Keyspan adapter does not have an aꢁached USB cable, aꢁach the included USB cable into the Keyspan
adapter’s USB port.
Step 5 – Connect the Adapter to Your USB Port.
Aꢁach the Adapter to your computer by connecꢀng the Adapter’s USB cable into any built-in USB port on your com-
puter or USB hub. It is necessary to turn off your computer when aꢁaching the Adapter.
Step 6 – Hardware Installaꢀon Complete!
Your Keyspan USB 4-Port Serial Adapter is ready for use now that you have installed hardware and soſtware.
4
4.1 – Configuring Your Serial Device
Prior to using your serial device (modem, UPS, etc.) with the Keyspan USB 4-Port Serial Adapter, you must:
1. Connect your serial device (hardware) to the Keyspan port.
2. Configure your serial device’s soſtware to use the Keyspan port.
Connecꢀng Your Serial Device (Hardware)
If your Keyspan adapter is not connected, please do so NOW.
Step 1 – Connect Your Serial Device to the Keyspan Adapter.
Aꢁach your serial device’s (Palm cradle, GPS, cell phone) serial cable to the serial port on your Keyspan USB 4-Port
Serial Adapter.
Step 2 – Determine Which Keyspan Port Your Serial Device is Connected To.
If you have a Keyspan product that has more than one serial port, please note which Keyspan serial port your serial
device is connected to (the serial port on the Keyspan product, not your USB ports on your computer or USB hub).
This informaꢀon will become useful as we start Configuring Your Serial Device’s Soſtware.
Configuring Your Serial Device’s Soſtware
The following configuraꢀon instrucꢀons provide a basic overview of how to configure your soſtware to use your
Keyspan serial port(s). For specific instrucꢀons on how to operate your serial device, please refer to your serial
device’s user manual for detailed instrucꢀons.
Step 1 – Check the Keyspan Serial Assistant.
Now that your serial device is connected to the Keyspan adapter, you should check to see if the Keyspan serial port is
installed correctly.
To do this, open the Keyspan Serial Assistant (in START menu -> PROGRAMS-> Keyspan USB 4-Port Serial Adapter ->
Keyspan Serial Assistant). When you open the Keyspan Serial Assistant, you will see the following window:
If your Keyspan hardware and soſtware are installed correctly, you will see your adapter in the ‘Adapter Status’ tab
box. You should also see the COM port number (COM1, COM2, etc.) and the COM Port Status (IDLE or BUSY).
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4.1 – Configuring Your Serial Device
The COM port number and its COM port status message are very important to configuring your serial device.
The COM port status is the state of the Keyspan serial port. All serial ports have two states, BUSY (In Use) or IDLE
(Available). When the serial port is IDLE, the port is available for use by any serial device’s soſtware. When a COM
port is BUSY, the serial port is in use by soſtware and therefore not available to other programs.
The COM port number is the address of the Keyspan serial port. In order for any serial device to communicate via
the Keyspan adapter, that serial device’s soſtware must be told to use the Keyspan COM port number.
Step 2 – Determine Where to Select/Configure the Keyspan Serial Port(s).
Prior to using your serial device with a Keyspan serial port, you must first tell that serial device’s soſtware which
serial port your serial device hardware is connected to.
For example, if you have a Palm, you will have to tell the Palm Desktop soſtware to look for your Palm handheld
(hardware) on a Keyspan serial port. By doing this, you establish communicaꢀon between your serial device’s
soſtware (the Palm Desktop soſtware) and your serial devices hardware (the Palm handheld unit).
Most serial devices will have soſtware that will allow you to select which serial port the device is connected to.
Depending on your serial device and its soſtware, you may have to configure: a Control Panel (modems accessing
ISPs), an applicaꢀon (UPS systems), or some combinaꢀon of these (modems accessing terminals using Zterm).
Please refer to your serial devices’ documentaꢀon on which method your serial device uses and how to access that
soſtware’s serial port “configuraꢀon” screen.
Once you’re determined where to select or configure your serial device’s soſtware’s serial port seꢂngs, please
proceed to Step 3.
Step 3 – Determine Which Serial Port to Select in Your Serial Device’s Soſtware.
When you’ve found the port selecꢀon screen in your serial device’s soſtware, you may be presented with a list of
COM port numbers, a place to type in a COM port number, or some combinaꢀon of both.
At this point, you have to select or enter the COM port number of the Keyspan serial adapter you are connecꢀng to.
Please note that you can see the COM port number in the Adapter Status tab in the Keyspan Serial Assistant.
Step 4 - Use Your Serial Device.
Once you’ve configured your serial soſtware to use the Keyspan serial port, you’re ready to start using your serial
device.
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5.1 – Keyspan Serial Assistant
Besides the required drivers, the Keyspan USB 4-Port Serial Adapter soſtware installer installs an applicaꢀon called
Keyspan Serial Assistant. This applicaꢀon is used to:
· Determine the status of the adapter soſtware and hardware
· Assist in problem solving
Launching the Keyspan Serial Assistant
To launch the Assistant, open the Keyspan Serial Assistant (in START menu-> PROGRAMS-> KEYSPAN USB 4-PORT
SERIAL ADAPTER-> KEYSPAN SERIAL ASSISTANT). When you open the Keyspan Serial Assistant, you will see the
following window:
If your Keyspan hardware and soſtware are installed correctly, you will see your adapter in the ‘Adapter Status’ tab
box. You should also see FOUR COM port numbers (COM1, COM 2, etc.) and their COM port status (IDLE or BUSY).
Explanaꢀon of Assistant Features
The following is a descripꢀon of all the relevant text boxes and menus found in the Keyspan Serial Assistant. You can
also obtain this informaꢀon by turning on the ‘Enable Tool Tips’ check box in the Help tab in the Assistant window.
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5.1 – Keyspan Serial Assistant
Adapter Status Tab
The Adapter Status tab in the Keyspan Serial Assistant displays the status of your Keyspan adapter. Specifically,
it shows the COM port number (COM1, COM2, etc.) and the COM port status (IDLE or BUSY). If you have several
Keyspan adapters of the same type, they will all show up in this tab.
This is also the first place to check to see if your Keyspan adapter is working properly.
Properꢀes Tab
The Properꢀes tab in the Keyspan Serial Adapter allows you to test your Keyspan adapter and make changes to the
behavior of the Keyspan adapter. The following is an explanaꢀon of the items in this tab:
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5.1 – Keyspan Serial Assistant
The Adapter pull down menu is used to select which USB 4-Port Serial Adapter you would like to configure. If you
only have one Keyspan USB 4-Port Serial Adapter, you will not need to change the selecꢀon.
The Power radio buꢁons are used to configure which USB power mode the Keyspan adapter will use.
Use the Low/Compaꢀble (normal speed) seꢂng when you are using mulꢀple serial devices at speeds of 115 Kbps or
lower or when only using one port at speeds of 230 Kbps or greater.
Use the High (high speed) seꢂng when you are using mulꢀple serial devices at speeds of 230 Kbps or greater.
The default seꢂng is Low/Compaꢀble (normal speed).
Please Note: Using the High Power (high speed) seꢀng requires that your Keyspan adapter be connected to a built-in
USB port on your computer or a self-powered USB Hub.
The Endpoints radio buꢁons are used to configure how the Keyspan adapter will communicate with the USB
subsystem (soſtware) on your computer. Most users will not need to modify the default seꢂng (High Performance
(BULK)). You should only change this seꢂng if you are sure that your serial device needs a specific seꢂng.
If you have more than one serial port on your Keyspan adapter, the Port pull down menu allows you select which
serial port you want to modify or test. You can also see the serial port’s COM port number and its COM port status
next to the Port pull down menu.
The Test This Port buꢁon tests the selected COM port in the Port pull down menu. The test that is performed is the
selected test in the Test Opꢀon box. The Test All Ports on this Adapter tests all of the COM ports on the selected
adapter in the Adapter pull down menu.
The Test Mode box allows you to specify the type of test that will be preformed when you press the Test This Port
buꢁon.
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5.1 – Keyspan Serial Assistant
There are 3 types of tests:
TX Only: Use this test to test only the transmit (Tx) signals of the Keyspan adapter.
Ext. LoopBack: Use this test for sending and receiving data. This test sends data out the selected serial port and
waits to receive it via a special Loopback connector. You can find more informaꢀon about this special Loopback
connector in the Serial Port Pin Outs secꢀon in this manual.
Int. LoopBack: Use this test for sending and receiving data. This test is performed within the Keyspan adapter
hardware. This test DOES NOT require a special Loopback cable.
The Test Type box allows to specify how many ꢀmes the selected test will be repeated when you press the Test
buꢁon. Use the Quick opꢀon to perform the test once. To perform a subsequent test, press the Test This Port buꢁon.
Use the Conꢀnuous opꢀon to repeat the test conꢀnuously. To stop the test, press the Stop Test buꢁon (the Test This
Port buꢁon becomes the Stop Test buꢁon during a test).
The Test Speed pull down menu allows to specify the speed (baud rate) at which the port will be tested at when you
press the Test This Port buꢁon.
The Test Status box reports the test status or results of the selected COM port.
The Receive FIFO Buffer Size pull down menu allows you to configure the number of characters which are stored in
the card’s “First In First Out” input buffer (“FIFO”) before they are made available to the computer. The default value
of this parameter is “16”. The Receive FIFO improves the reliability of data transfer at high speeds. You can turn this
opꢀon OFF for performance reasons however this is not necessary in most cases.
The Enable Remote Wakeup check box allows you to specify if you want your computer to ‘wake up’ from SLEEP/
SUSPEND mode.
Remote wakeup is provided via the RI (ring indicator) pin (see the Serial Port Pin Outs appendix of the device).
Note: Remote Wakeup is enabled on a per-port basis.
The Update Configuraꢀon buꢁon updates the Keyspan adapter with the changes you have made in the Properꢀes
tab. Please note that these changes will take effect when you click the Update Configuraꢀon buꢁon.
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5.1 – Keyspan Serial Assistant
Port Mapping Tab
The Port Mapping tab in the Keyspan Serial Assistant allows you to change how COM port numbers are assigned to
your Keyspan adapter. The following is an explanaꢀon of the item in this tab.
Important!!! Please make sure you read this enꢀre secꢀon. Changing COM port assignments may render other
hardware unusable.
The COM Port List box shows any connected Keyspan USB 4-Port Serial Adapter, its COM port numbers and COM port
statuses. You can also see any other COM ports that have been assigned or reserved on your computer if you enable
or check the Show All COM Assignment check box.
Enable or check the Show All COM Assignments check box to display ALL of the COM port name and numbers that
have been registered on your computer. This will include COM ports for other devices.
Note: You may have COM ports assigned or ‘set aside’ for hardware that may not be installed on your computer
depending on how your computer was setup by its manufacturer.
The COM port mapping pull down menu allows you to reassign the selected Keyspan COM port in the COM port list
window. This window also reports whether a COM port is ‘in use’. In this menu, ‘In use’ means that the selected COM
port has been assigned or reserved. It is highly recommended that you only change the COM port mapping to COM
ports that are not ‘in use’.
Note: The Com port mapping pull down menu allows you to change the COM port mapping to any COM port
including those that have already been assigned (aka in use). Changing the COM port mapping to a COM port that is
in use may render any hardware and/or soſtware using that port inoperable.
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5.1 – Keyspan Serial Assistant
The Adapter Port Mapping Mode box allows you to change the behavior of how Keyspan COM port numbers are
assigned when you connect the Keyspan adapter to a different USB port than the one it was originally connected to.
Dynamic assigns a COM port number (or numbers if your Keyspan adapter has mulꢀple serial ports) to a parꢀcular
Keyspan adapter. If you disconnect the Keyspan adapter and connect it to a different USB port, the COM port number
of that Keyspan adapter will not change. This is the default seꢂng and is recommended seꢂng if you only have one
Keyspan adapter.
Geographic assigns a COM port number (or numbers if your Keyspan adapter has mulꢀple serial ports) to a parꢀcular
USB port on your computer. If you disconnect the Keyspan adapter and connect it to a different USB port, the COM
port number of that Keyspan adapter will change. This seꢂng is recommended if you are using mulꢀple Keyspan
adapters and want the COM port numbers to remain the same.
The Delete All Keyspan USB 4-Port Serial Adapter Port Mappings buꢁon clears the Windows registry of all Keyspan
USB 4-Port Serial Adapter COM port numbers and Keyspan USB informaꢀon. This allows Windows to create new
COM port assignments.
Note: This is an opꢁon for advanced users only.
Diagnosꢀcs Tab
The Diagnosꢀc tab in the Keyspan Serial Assistant reports diagnosꢀc informaꢀon about your Keyspan adapter’s
soſtware and hardware this informaꢀon is useful if you are trying to solve problems with Keyspan’s technical support
staff. The following is an explanaꢀon of the items in this tab.
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5.1 – Keyspan Serial Assistant
The Adapter Status/Error Events box displays the status of your Keyspan adapter hardware and soſtware. It detects
if the Keyspan driver is installed and whether or not a Keyspan adapter is connected.
The Clear Log Window buꢁon will clear the Adapter Status/Error Events box.
Enable or check the Log Debug Events check box to display all of the Keyspan adapter’s debug events as well as the
driver events. This opꢀon can be turned on and off.
The Open Driver Events Windows buꢁon will open the Keyspan adapter’s Event log window. This window reports
all of the events or acꢀons that the adapter is performing. This is useful in troubleshooꢀng data communicaꢀon
problems.
The Open Data Monitor Window buꢁon will open the Keyspan adapter’s Line Monitor (Data Monitor) window.
The Line Monitor will display all data and all modem control state changes sent to and from the USB 4-Port Serial
Adapter.
Help Tab
The Help tab in the Keyspan Serial Assistant displays the version numbers of the different components in your
Keyspan USB Serial Adapter installaꢀon. You can also enable Tool Tips (on screen help).
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6.1 – Problem Solving
If you are having problems with your Keyspan USB to Serial Adapter, please read the following instrucꢀons to assist
you in troubleshooꢀng.
Hardware Troubleshooꢀng
Step 1 – Use the Keyspan Serial Assistant.
Launch the Keyspan serial Adapter applicaꢀon. When you open the Keyspan serial Assistant applicaꢀon, the ‘Adapter
Status’ tab will show your Keyspan adapter, its COM port numbers (COM1, COM2, etc.) and its COM port status (IDLE
or BUSY).
Soſtware/Serial Device Troubleshooꢀng
Step 1 – Check the Physical Connecꢀons.
Make sure that your serial device is powered on and is properly connected to the Keyspan Serial Adapter.
Step 2 – Check Your Serial Device’s Soſtware Configuraꢀon.
Check to see if your serial device’s soſtware is configured to use the Keyspan port. Please refer to your serial device’s
documentaꢀon for instrucꢀons on how to select/switch/configure a serial port in that soſtware.
Once you’ve found your soſtware port configuraꢀon screen, it should display the Keyspan USB 4-Port Serial Adapter
COM port number.
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7.1 – Appendices
· Frequently Asked Quesꢀons (FAQs)
Frequently Asked Quesꢀons
· Configuraꢀon Examples for Windows
Instrucꢀons on configuring select serial devices to use Keyspan serial ports
· Serial Port Pin Outs
Serial Port Pin Out and loopback Test Informaꢀon
· LED Behavior
Descripꢀon of the LED Behavior on your Keyspan Adapter
· TX Ack Advance
White Paper on the TX Ack Advance feature
7.1.a – Frequently asked Quesꢀons (FAQs)
The following is a list of Frequently Asked Quesꢀons (FAQs) about Keyspan USB 4-Port Serial Adapter:
Quesꢀon:
How do I configure my serial device to recognize the Keyspan USB 4-Port Serial Adapter?
Answer:
To configure any serial device to use a serial port on any Keyspan USB Serial Adapter, you must:
1. Locate the soſtware that controls your serial device.
2. Access that soſtware’s port or connecꢀon configuraꢀon screen/dialog/menu/etc.
3. Select the Keyspan port that your device is connected to in port or connecꢀon configuraꢀon screen/
dialog/menu/etc. for that device.
Depending on what type of serial device you have, you may have to configure a control panel, an applicaꢀon, or a
plug-in.
Quesꢀon:
Can I connect my Keyspan USB device to a USB hub?
Answer:
Yes, any Keyspan USB device can be connected to a USB hub. However, there are some USB hubs that cannot fully
support some USB devices. If you are having problems with a Keyspan USB device that is connected to a USB hub,
please connect the Keyspan USB device to a built-in USB port on your computer. If this solves the problem, then this
may be an issue with your USB hub.
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7.1.b – Configuraꢀon Example for Windows
The following is a configuraꢀon example for Windows. The example provides step-by-step instrucꢀons on configuring
select serial devices.
· Palm Desktop
7.1.c – Palm Desktop
Before you begin…
This configuraꢀon example assumes that you have already done the following:
1. Installed the Keyspan serial port hardware and soſtware.
2. Installed the Palm Desktop soſtware.
3. Connected the Palm Serial Cradle hardware to a Keyspan serial port.
If you have not performed any of the steps menꢀoned above, please do so before proceeding.
Step 1 – Check the Keyspan Serial Assistant.
Before proceeding, you should check to see if the Keyspan serial port is installed correctly.
To do this, open the Keyspan Serial Assistant (in Start menu-> Programs-> Keyspan USB 4-Port Serial Adapter->
Keyspan Serial Assistant). When you open the Keyspan Serial Assistant, you will see a window similar to the one
shown below:
If your Keyspan hardware and soſtware are installed correctly, you will see your adapter in the ‘Adapter Status’ tab
box. You should also see the COM port number (COM1, COM2, etc.) and the COM port status (IDLE or BUSY).
Step 2 – Access the HotSync ® Manager.
Before you can begin to HotSync your Palm, you must access and configure the HotSync® Manager applicaꢀon. The
Hotsync Manager is the program that manages the serial communicaꢀon between your Palm and your computer.
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7.1.c – Palm Desktop
The easiest way to access the HotSync Manager is via the Palm Desktop soſtware. To do this, launch the Palm
Desktop soſtware. When the Palm Desktop soſtware is running, go to the “HotSync” menu and select the “Setup”
command.
Once the HotSync® Manager applicaꢀon is opened, you will be presented with the HotSync Setup window.
Step 3 – Configure the HotSync setup Window.
In the HotSync Setup window, click on the Local tab. This will display the Serial Port and Speed pull down menus.
Select you Keyspan COM port in the Serial Port pull down menu (see step 1 in this example).
Select ‘As Fast As Possible’ from the Speed pull down menu.
Step 3 – HotSync Your Palm Organizer.
Palm Soſtware configuraꢀon is now complete. To iniꢀate a ‘HotSync’ session, place your Palm Organizer in its cradle
and then press the HotSync buꢁon on the cradle. Your Palm Organizer will now “HotSync”.
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7.1.d – Serial Port Pin Outs
The pin assignments for the Keyspan USB 4 Port serial Adapter’s male DB9 port are illustrated below:
Pin
1
Name
DCD
RX
Signal Designaꢀon
Data Carrier Detect (Input)
Received Data (Input)
Transmiꢁed Data (Output)
Data Terminal Ready (Output)
Ground
2
3
TX
4
DTR
GND
DSR
RTS
CTS
RI
5
6
Data Set Ready (Input)
Request To Send (Output)
Clear To Send (Input)
Ring Indicator (Input)
7
8
9
In order to ensure compliance with emission specificaꢀons, cables, should be shielded using braided shields and
metal hoods with complete 100% contact between the shields and hoods.
External Loopback Connector Informaꢀon
The Keyspan Serial Assistant allows you to perform two types of loopback tests – internal and external. The external
test requires the use of a special loopback connector. This connector requires a “DB9 Female Loopback plug” with
the following wiring:
Pin(s) Wired to
Pin(s)
4, 8
3
1
2
6
<->
<->
<->
7, 9
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7.1.e – LED Behavior
The Keyspan USB 4-Port Serial Adapter part number USA-49WG comes equipped with LED lights that report the
status of the Keyspan adapter USB hardware and serial port.
The following table shows all of the possible states of these LED light and what they mean:
Color
State
Significance
Red
Off
The Keyspan adapter is not connected or not receiving power from your
computer.
Red
On
The Keyspan adapter is connected and is receiving power from your
computer.
Green
Green
Green
Off
The Keyspan adapter soſtware and hardware are working properly.
(and Red light ON) The Keyspan serial port is available for use.
On-Steady Light
The Keyspan serial port is ‘in use’ by an applicaꢀon on your computer and
is ready to send and receive data to and from your serial device.
On-Blinking Rapidly The Keyspan serial port is sending and/or receiving data.
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7.1.f – TX ACK Advance
Overview
Many Keyspan USB serial adapters support confirmable “Transmit Acknowledgement Advance” (aka TX-ACK threshold,
aka TX-ACK (nowledgement) advance, etc.) in the Keyspan Manager. This feature allows the user to adjust a device’s
transmit behavior to achieve the opꢀmum compromise between compaꢀbility (exact emulaꢀon of built-in ports) and
maximum throughput. This document describes the factors which a user should be aware of to guide their configuraꢀon
of this feature.
The Problem
In the case of a standard, “built-in” serial port, the host CPU (the “brain” of the computer) can communicate directly
with the serial hardware because the (serial) hardware is in the address space directly accessible to the CPU. When
the serial port has transmiꢁed all the data in its transmit FIFO (the buffer that holds characters waiꢀng to be sent), it
interrupts the CPU, which then adds more characters to the transmit FIFO with a minimum ꢀme delay.
By contrast, in a USB to serial adapter situaꢀon, informaꢀon about the state of the serial port FIFO reaches the CPU
by means of USB messages. The USB subsystem in most computers delays the delivery of inbound (USB peripheral to
USB host computer) USB messages by about 1 millisecond. The impact of this delay on serial throughput depends on
the baud rate. At 9600 baud, it takes about 1 millisecond to transmit a character. If the serial adapter signals the host
when it begins transmiꢂng the last character in its FIFO, the host learns about it at about the same ꢀme the character
is actually finished being transmiꢁed. Since outbound (USB host computer to USB peripheral) USB messages are not
subject to such a long delay, the host can supply new data before the serial port has been idles for too long.
At higher baud rates, however, this 1-millisecond delay becomes more of a problem. For example, at 920 Kbps, 1
millisecond is enough ꢀme to send 92 characters. So, if you’re sending 92 characters at a ꢀme, you will only achieve
50% throughput, since half the ꢀme is spent with the adapter waiꢀng for the host to send more data.
The Work Around
Since there’s no way to eliminate the USB delays, there’s only one work around: the serial adapter has to like about
when it’s done transmiꢂng. The size of the lie is what’s being configured with the “TX Ack Advance” parameter: it
specifies how many characters ahead of ꢀme the adapter tells the host “I’m done.” This way, the adapter sꢀll has some
data to transmit while it’s waiꢀng for more to arrive from the host. If the next data from the host arrives before the
previous data is completely sent, the new data can be sent with no delay, and the device will achieve 100% transmit
throughput.
Notes about the Work Around
In most situaꢀons, the serial adapter’s lie is harmless or beneficial, even. However, in some circumstances, this lie gets
us into trouble. There are several ways this can happen:
Flow control: If the adapter is programmed to use flow control, the remote (receiving) end of the serial connecꢀon can
ask the adapter to suspend its data transmission (e.g. if it’s not ready to receive more data). Since this state can persist
indefinitely, the “I’m done” indicaꢀon, if it were sent early, could arrive at the host a significant amount ahead of ꢀme.
As a result, the applicaꢀon might use the “I’m done” signal as an indicaꢀon that the remote end is ready, leading to
various kinds of trouble.
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7.1.f – TX ACK Advance
Data flushing: Someꢀmes, an applicaꢀon will issue a “transmit flush” command to the adapter to get rid of extra data.
For example, let’s say an applicaꢀon sends “AAAA” to the adapter, and then, once it’s received the “I’m done” indicaꢀon
sends “BBBB.” Now, let’s say that someꢀme aſter sending “BBBB,” the applicaꢀon decides to cancel whatever part of
the ‘BBBB” has yet to leave the serial port, and sends a “transmit flush” command to the adapter. If the adapter had
been lying about being done sending “”AAAA,” it might sꢀll not be done, and the flush could purge the transmit FIFO
of some of the A’s (which is not what the applicaꢀon was expecꢀng) in addiꢀon to the B’s.
Timing: In some applicaꢀons, the receipt of the “I’m done” indicaꢀon is used as a ꢀming reference point. For example,
an applicaꢀon could send a data stream like this:
COMMAND…………………………………………………….
The extra periods following COMMAND would be just used to establish a ꢀming interval: the applicaꢀon would know
that once the serial port said “I’m done,” the receiver would have had at least 64 character ꢀmes to process COMMAND.
If the “I’m done” indicaꢀon was sent early, the applicaꢀon might then do it’s subsequently acꢀon too early.
Another possibility is that the applicaꢀon is using the ꢀming of the “I’m done” message to determine the baud rate. For
example, if the serial port was using external clocking, the applicaꢀon might not know what baud rate was being used,
so it would send a message and see how long it took. The early delivery of “I’m done” could screw up its calculaꢀon.
There are many other communicaꢀon protocols in which ꢀme periods are counted from the point that message has
been delivered. Any ꢀme you change the ꢀming of the “I’m done” indicaꢀon, you run the risk if interfering with such
protocols.
What Should I Use?
There are various way to configure Tx Ack Advance. Following is a discussion of some possibiliꢀes:
None: If you’re using a baud rate of 9600 or less, you probably don’t have a problem. The 1 millisecond delay will not
significantly affect your throughput, and you can select this opꢀon. This opꢀon is also a good choice if you are running
an applicaꢀon in which throughput is not an issue, or one in which guaranteeing 100% correct operaꢀon is important
enough that you’d prefer not to risk having problems.
Auto: The ‘Auto” seꢂng uses that calculaꢀon described above when internal clocking is used and sets the Tx Ack
Advance to “None” when external clocking is used (this is because the host doesn’t know the baud rate when the
clocking is supplied externally).
Experiment: If you’re using a baud rate above 9600, you can simply try increasing the Tx Ack Advance seꢂng, and
see whether it improves performance 9in which case, great!), causes problems (in which case, don’t use it) or doesn’t
make any difference (in which case it doesn’t maꢁer what you do).
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7.1.f – TX ACK Advance
Calculate: If you know that your applicaꢀon will not run into trouble with flow control or data flushing, you know what
baud rate it uses, and you’d like to adjust the Tx Ack Advance to most closely approximate the ꢀming of a built-in port,
you can calculate the value yourself using this formula:
Integer ( (baud / (totalBitsPerCharacter * 1000)) + 0.5)
This will result in the host receiving the “transmit complete” message at approximately the same ꢀme the last character
has actually been transmiꢁed. Note: the total bits per character include the start bit, the stop bit(s), the parity bit (if
any) and the data bits. So, an 8-bit character with one stop bit and no parity has a total of 10 bits.
2-Year Limited Warranty
TRIPP LITE warrants its products to be free from defects in materials and workmanship for a period of two (2) years from the date of iniꢀal purchase. TRIPP LITE’s
obligaꢀon under this warranty is limited to repairing or replacing (at its sole opꢀon) any such defecꢀve products. To obtain service under this warranty, you must
obtain a Returned Material Authorizaꢀon (RMA) number from TRIPP LITE or an authorized TRIPP LITE service center. Products must be returned to TRIPP LITE or
an authorized TRIPP LITE service center with transportaꢀon charges prepaid and must be accompanied by a brief descripꢀon of the problem encountered and
proof of date and place of purchase. This warranty does not apply to equipment which has been damaged by accident, negligence or misapplicaꢀon or has been
altered or modified in any way.
EXCEPT AS PROVIDED HEREIN, TRIPP LITE MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE. Some states do not permit limitaꢀon or exclusion of implied warranꢀes; therefore, the aforesaid limitaꢀon(s) or exclusion(s) may not
apply to the purchaser.
EXCEPT AS PROVIDED ABOVE, IN NO EVENT WILL TRIPP LITE BE LIABLE FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USE OF THIS PRODUCT, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Specifically, TRIPP LITE is not liable for any costs, such as lost profits or
revenue, loss of equipment, loss of use of equipment, loss of soſtware, loss of data, costs of subsꢀtutes, claims by third parꢀes, or otherwise.
WARRANTY REGISTRATION
win a FREE Tripp Lite product!*
* No purchase necessary. Void where prohibited. Some restricꢀons apply. See website for details.
Warning!
Use of this equipment in life support applicaꢀons where failure of this equipment can reasonably be expected to cause the failure of the life support equipment
or to significantly affect its safety or effecꢀveness is not recommended. Do not use this equipment in the presence of a flammable anestheꢀc mixture with air,
oxygen or nitrous oxide.
FCC Noꢀce, Class B
This device complies with part 15 of the FCC Rules. Operaꢀon is subject to the following two condiꢀons: (1) This device may not cause harmful interference, and
(2) this device must accept any interference received, including interference that may cause undesired operaꢀon.
Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are
designed to provide reasonable protecꢀon against harmful interference in a residenꢀal installaꢀon. This equipment generates, uses and can radiate radio
frequency energy and, if not installed and used in accordance with the instrucꢀons, may cause harmful interference to radio communicaꢀons. However, there is
no guarantee that interference will not occur in a parꢀcular installaꢀon. If this equipment does cause harmful interference to radio or television recepꢀon, which
can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separaꢀon between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.
Any changes or modificaꢀons to this equipment not expressly approved by Tripp Lite could void the user’s authority to operate this equipment.
WEEE Compliance Informaꢀon for Tripp Lite Customers and Recyclers (European Union)
Under the Waste Electrical and Electronic Equipment (WEEE) Direcꢀve and implemenꢀng regulaꢀons, when customers buy new electrical and electronic
equipment from Tripp Lite they are enꢀtled to:
• Send old equipment for recycling on a one-for-one, like-for-like basis (this varies depending on the country)
• Send the new equipment back for recycling when this ulꢀmately becomes waste
Tripp Lite follows a policy of conꢀnuous improvement. Product specificaꢀons are subject to change without noꢀce.
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