Taking full advantage of the GGLABS T232

The GGLABS T232 is very popular for debugging legacy RS-232 connections. In this article we will describe a few debugging tips and show how to emulate some of the common cable configurations.

T232 Pin assignments

Dip Switch DE-9 Pin Name Description
1 2 RxD Receive Data
2 3 TxD Transmit Data
3 8 CTS Clear to Send
4 7 RTS Request to Send
5 6 DSR Data Set Ready
6 4 DTR Data Terminal Ready
7 1 DCD Data Carrier Detect
8 9 RI Ring Indicator
- 5 GND Ground

9-wire Straight (Default Configuration)

All dip switch onNo Jumpers
All dip switch on. No additional jumpers.

This is a 9-wire standard straight through cable. It's used to connect a host computer (DTE) to a modem or other device configured as a DCE.

3 wire straight configuration

All dip switch onNo Jumpers

Dip 1 and 2 on. No additional jumpers.
This configuration emulates a 3 wire (no hardware flow control) straight cable.

5 wire straight configuration

All dip switch onNo Jumpers
Dip 1-4 on. No additional jumpers.
This configuration emulates a 5 wire (CTS/RTS flow control) straight cable.

3 wire straight with handshake shorts

All dip switch on3 wire straight with shorts
Dip 1 and 2, jumpers as shown.
This configuration is useful when connecting a device (DCE) with no handshake with a computer (DTE) that can't turn off flow control.

Minimal (3 wire) Null Modem

All dip switch on3 wire null modem
All dip off, jumpers as shown.
Null modem cabling is required to connect two DCE (computers) to each other. In it's simplest configuration only TxD and RxD are swapped.

5 wire null modem

All dip switch on5 wire null modem
All dip off, jumpers as shown.
Null modem with hardware flow control.

Full Null Modem

All dip switch onFull null modem
All dip off, jumpers as shown.
Null modem with full handshake (hardware flow control and modem lines).

3 wire Null Modem with CTS/RTS shorts

All dip switch on3 wire null modem with shorts
All dip off, jumpers as shown.
Useful to connect two DTE when one expects hardware flow control and the other one does not support it.

3 wire Null Modem with full handshake shorts

All dip switch on3 wire null modem with shorts
All dip off, jumpers as shown.
Useful to connect two DTE when one expects a DCE type device and the other one can't fully emulate a DCE.

5 wire null modem with shorts

All dip switch on5 wire null modem with shorts
All dip off, jumpers as shown.
Similar to the previous one with the addition of hardware flow control.

3 wire loopback

All dip switch on3 wire loopback
All dip off, jumpers as shown.
Simplest loopback cable.

5 wire loopback

All dip switch on5 wire loopback
All dip off, jumpers as shown.
Loopback cable with support for hardware flow control.

Full loopback

All dip switch onfull loopback
All dip off, jumpers as shown.
Loopback cable with full modem emulation.

Diagnostic loopback

All dip switch ondiagnostic loopback
All dip off, jumpers as shown.
Loopback cable to use with diagnostic software.

glossary

DTE: Data Terminal Equipment (usually the computer)
DCE: Data Communication Equipment (traditionally a modem)

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