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Pin Assignments for HP Serial Cables

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Pin Assignments for HP Serial Cables

Refer to this document for information about:

•  The standard pin functions (RS-232 standard)•  The pin assignments for HP Serial Cables, DB-9 and DB-25

RS-232 Standard Pin FunctionsThe RS-232 standard identifies pin assignments and functions for serial cable connections, using a 25-pin

serial connector as the basis for the assignments. This list includes all of the functions designated by thestandard, although HP does not use all of these pins in its printer side connectors.

Pin 1 - Protective GroundThis pin is also referred to as chassis ground. It provides protection against electrical shock where two

pieces of equipment are connected and one piece does not include a ground connection (the round prong

on the plug that goes in the electrical outlet). In some cases, not connecting the chassis ground maydisable communication. Sometimes connecting these pins may create a problem known as ground loop (a

short), where the equipment behaves erratically. Both of these situations are rare. In most cases, pin 1 isnot needed to establish communication between two devices.

Pin 2 - Transmit data (TxD or TD)Pin 2 is used to transmit data from the printer to the computer. The transmit data pin on the printer

should be connected to the receive data pin on the computer.

Pin 3 - Receive data (RxD or RD)Pin 3 is used to receive data from the computer to the printer. The receive data pin on the printer should

be connected to the transmit data pin on the computer.

Pin 4 - Request to Send (RTS)

Pin 4 is a general purpose output on the computer. It is used by modems to signal a desire to transmit

data. Even though HP printers send a high voltage on pin 4 when the printer is powered up, they do notrequire RTS to function. Because of this, pin 4 is not listed in the pin outs for HP printers. Some

mainframes look to pin 4 (pin 1 on the 9 pin serial connectors) to determine that the printer is there.

Pin 5 - Clear to Send (CTS)

Pin 5 is a general purpose input on the computer. HP printers do not require CTS to function.

Pin 6 - Data Set Ready (DSR)

Pin 6 is a general purpose input on the printer to signal that the computer is powered up and ready to go.

HP printers do not require DSR to function.Pin 7 - Common (Signal Ground)

Pin 7 is a reference point for all interface voltages. It enables the devices at both ends of the cable to havethe same definition for voltage levels, such as +5 volts for both devices.

Pin 8 - Data Carrier Detect (DCD)

Pin 8 allows the computer to signal when it’s made a connection to a modem. HP printers do not requirethe DCD to function.

Pin 20 - Data Terminal Ready (DTR)Pin 20 is a general purpose output on the printer. When connected to CTS and DSR on the computer, it

signals that the printer is powered up, on line, and ready to receive data.

DB-9 Serial Cable (HP C2932A)

Computer DB-9 Printer DB-9 (male end)

2 Receive Data 2 Transmit Data3 Transmit Data 3 Receive Data

4 Data Terminal Ready (DTR) 4 Data Set Ready (DSR)

5 Ground 5 Ground6 Data Set Ready 6 Data Terminal Ready

8 Clear to Send (CTS) 8 Data Terminal Ready

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Pin Assignments for HP Serial Cables

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DB-25 Serial Cable (HP C2933A)

Computer DB-9 Printer DB-9 (male end)

2 Receive Data 2 Transmit Data

3 Transmit Data 3 Receive Data

20 Data Terminal Ready 4 Data Set Ready7 Ground 5 Ground

6 Data Set Ready 6 Data Terminal Ready5 Clear to Send 8 Data Terminal Ready

The tables above list only those pins used by the printer for communication. Unlisted numbers areunassigned. The pin outs for the computer end are typical pin numbers; actual numbers may vary.

Copyright © Hewlett-Packard Co. 2002 This information is subject to change without notice and is provided "as is" withno warranty. Hewlett-Packard shall not be liable for any direct, indirect, special, incidental or consequential damages inconnection with the use of this material.