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).

Implementations

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:

• With DMA (Direct Memory Access)
  • ASCII MSX-Serial 232
• Without DMA
  • Repro Factory HBI-232MKII
  • Sony HB-G900
  • Sony HBI-232

Hardware

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: http://www.msxarchive.nl/pub/msx/mirrors/msx2.com/sources/rs232msx.zip

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").

Check also the pages about

• the RS-232C port: RS-232C port
• the RS-232C Interfaces: RS-232C Interfaces