This page was last modified 15:34, 13 January 2022 by Mars2000you.

RS-232C is an optional part of the MSX standard, as such very few MSX systems have it built in. It uses one or several UART chips on a serial card or interface (UART = Universal Asynchronous Receiver / Transmitter).



There are two implementation versions for the MSX:

RS-232C v1

RS-232C v1 is the first implementation, and the most common. It uses I/O ports for communication.

Only one RS-232C v1 interface may be present at a time, having more then one installed may even cause damage to both interfaces as they will share the same I/O ports.

The Russian RS-232C (in Yamaha YIS-503IIR computer) is different in I/O adressing, it uses port 00h to 07h.

RS-232C v2

RS-232C v2 is the second implementation. It uses memory mapped I/O. Because of this, more then one interface can be present at the time. It is also possible to mix a single RS-232C v1 interface with a RS-232C v2 interface.

The maximum number of RS-232C cartridges is unclear, some say 4 other interfaces, other say it can be up to 9 devices.

The only implementations of RS-232C BIOS 2.0 are:


Official ASCII documentation for the MSX Serial interface with the RS-232C Extended BIOS Call specification, MSX RS-232C interface hardware specification and MSX RS-232 Control software 2.0 can be found in this zip file:

The C in RS-232C refers to the revision of the RS-232 standard, issued in a document dated August 1969 ("Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange").

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