Serial Port Pin Signal Tables

Serial Port Pin Signal Tables

The serial port on your workstation or server is either a DB-9 (9-pin) or a mini-DIN8 port. In either case, the port is clearly labeled as a serial port. Consult your system Owner's Guide to determine which kind of port your system has. There are two basic printer cable configurations; one for the DB-9 serial ports and one for the mini-DIN8 serial port. Depending on the cables used some serial functionality may be sacrificed due to unconnected wires in the cable. Note that the pinout of the DB-9 connectors is different from that of the full size DIN connectors that may be next to them. These DIN connectors also have different pinouts from the mini-DIN8 connectors used on some systems and documented in this section. The DB-9 and full-sized DIN connectors are connected to the same internal port hardware.

DB-9 Connector Cabling

For most serial printers, use the following cable. This cable uses the normal 3-wire connection and be used as a /dev/ttyd* device. Table 2-2 lists typical DB-9 serial pin assignment, as shown in Figure 2-5.

Figure 2-5 : DB-9 Pin Assignment

Pin Definitions for a DB-9 Serial Cable
DB-9-Male Function
1 Transmit Data
2 Receive Data
3
4
5
6
7 Signal Ground
8 Data Carrier Detect*
9

Pin Definitions for a DB-9 Serial Cable
DB-9-Male	Function
1	Transmit Data
2	Receive Data
3
4
5
6
7	Signal Ground
8	Data Carrier Detect*
9

* Data Carrier Detect is used only with /dev/ttym* devices if the system must notice when the printer powers off. Normally it is not used.

For printers using RTS/CTS hardware flow control, the following pinout allows "full flow control." This cable is required to implement /dev/ttyf* devices. This cable also supports /dev/ttym* devices. Table 2-3 lists the correct pinout for these devices, as shown in Figure 2-6.

Figure 2-6 : DB-9 to DB-25 RTS/CTS Flow Control Cable

Pin Definitions for a DB-9 to DB-25 RTS/CTS Flow Control Cable
DB-9-Male Signal DB-25-Male Signal
1 not used 1 not used
2 Transmit Data 2 Receive Data
3 Receive Data 3 Transmit Data
4 Request to Send* 4 Request to Send*
5 Clear to Send* 5 Clear to Send
6 not used 6 not used
7 Signal Ground 7 Signal Ground
8 Data Carrier Detect 8 Data Carrier Detect
9 Data Terminal Ready 20 Data Terminal Ready

Pin Definitions for a DB-9 to DB-25 RTS/CTS Flow Control Cable
DB-9-Male	Signal	DB-25-Male	Signal
1	not used	1	not used
2	Transmit Data	2	Receive Data
3	Receive Data	3	Transmit Data
4	Request to Send*	4	Request to Send*
5	Clear to Send*	5	Clear to Send
6	not used	6	not used
7	Signal Ground	7	Signal Ground
8	Data Carrier Detect	8	Data Carrier Detect
9	Data Terminal Ready	20	Data Terminal Ready

* RTS and CTS are ignored (optional) if using /dev/ttym* but required if using /dev/ttyf*.

Note: This cable can be used with a null modem adapter for printers; however, it is recommended that you use this cable exclusively for modem connections. The IBM pC/AT to modem cable ("off the shelf cable") does not work properly with your workstation. For additional information, see the serial(7) reference page.

Mini-DIN8 Connector Cabling

Many workstations and servers use the mini-DIN8 serial port. Check your system Owner's Guide to see if your system supports this type of connection. Note that the pinout of these mini-DIN8 connectors is different from that of the DIN connectors on larger systems. These larger systems also have DB-9 connectors that are connected to the same internal port hardware.

For most serial printers you should use a commercially available cable, Macintosh SE to ImageWriter1. This cable uses the normal three-wire connection and is used as a /dev/ttyd* device. Table 2-4 lists the pin configuration, as shown in Figure 2-7.

Figure 2-7 : Mini-DIN8 to DB-25 Serial Cable

Pin Definitions for a Mini-DIN8 to DB-25 Serial Cable
Mini-DIN8-Male Signal DB-25-Male Signal
1 not used 1 not used
2 not used 2 Transmit Data
3 Transmit Data 3 Receive Data
4 Signal Ground 4 Request to Send
5 Receive Data 5 Clear to Send
6 not used 8 Data Carrier Detect*
7 Data Carrier Detect* 20 Data Terminal Ready
8 Signal Ground

Pin Definitions for a Mini-DIN8 to DB-25 Serial Cable
Mini-DIN8-Male	Signal	DB-25-Male	Signal
1	not used	1	not used
2	not used	2	Transmit Data
3	Transmit Data	3	Receive Data
4	Signal Ground	4	Request to Send
5	Receive Data	5	Clear to Send
6	not used	8	Data Carrier Detect*
7	Data Carrier Detect*	20	Data Terminal Ready
8	Signal Ground

* /dev/ttym* devices should be used with this cable only if the system must notice when the terminal or printer is powered off.

Note: A Macintosh SE cable has other pins connected, but they can be ignored.