RS-232 port
This page was last modified 19:33, 15 July 2019 by Mars2000you.

Contents

Description

The RS-232 port is the standard port for the RS-232 interface.

Only a few machines have this port as the RS-232 interface is optional in the MSX Standard Definition.

For the machines without this port:

  • this port will be present on an external interface inserted in a cartridge slot
  • this cartridge slot can also be a modem with built-in RS-232 interface
  • some Toshiba and Mitsubishi machines are conceived to integrate an internal RS-232 interface, sold as a kit to be build in the computer

For more details, check this page: RS-232 Interface

Two different connectors can be found on the MSX hardware for the RS-232 port: DB-25 and DE-9.

Pinouts

DB-25 port

Note: the table below lists the full pin mapping, however most (all?) implementations only implement the minimum to support a Modem or Terminal, as that is all that is required according to the MSX RS232 specification. As such you may find that only Pins 1-8, 20 and 22 are actually connected.

DB-25 Female diagram
DB-25 Male diagram


Pin Name Type Description
1 GND - Shield Ground
2 TXD O Transmit Data
3 RXD I Receive Data
4 RTS O Request to Send
5 CTS I Clear to Send
6 DSR I Data Set Ready
7 GND - System Ground
8 CD I Carrier detect
9 - Reserved
10 - Reserved
11 - Reserved
12 S.CD I Secondary Carrier Detect
13 S.CTS I Secondary Clear to Send
14 S.TXD O Secondary Transmit Data
15 TXC I Transmit Clock
16 S.RXD I Secondary Receive Data
17 RXC I Receive Clock
18 - Reserved
19 S.RTS O Secondary Request to Send
20 DTR O Data Terminal Ready
21 SQD O Signal Quality Detector
22 RI I Ring Indicator
23 DSRST O Data Signal Rate Selector
24 TSETT O Transmitter Signal Element Timing (External clock)
25 - Reserved

DE-9 port

This port is often, incorrectly, called DB-9. The correct name of the port is DE-9, and it is the same connector as used for the MSX Joystick port, although electrically incompatible!

DE-9 Female diagram
Pin Name Type Description
1 PG - Protective Ground
2 TXD O Transmit Data
3 RXD I Receive Data
4 RTS O Request to Send
5 CTS I Clear to Send
6 DSR I Data Set Ready
7 GND - Signal Ground
8 DCD I Carrier detect
9 DTR O Data Terminal Ready