Most, but not all, of the internal or external RS-232 interfaces come with a ROM containing additional MSX-BASIC instructions, see RS-232C BASIC for details. The interfaces without this specific ROM will not work with all serial applications.

MSX computers with integrated RS-232 interface

• Aucnet NIA-2001
• Daisen Sangyo MX-2021
• Mitsubishi ML-G3
• Mitsubishi ML-G30 Model 2 (no RS-232C rom)
• Pioneer UC-V102 (can be extended with two UK-V104 boards for a total of 5 RS-232 connectors)
• Sony HB-G900
• Spectravideo SVI-738
• Toshiba HX-22
• Toshiba HX-23F
• Toshiba HX-52
• Victor HC-90
• Victor HC-95
• Yamaha YIS-503IIR

MSX computers with optional RS-232 upgrades

Without RS-232C rom in the computer

The Mitsubishi ML-G30 Model 1 is designed to be up-gradable with a kit, the Mitsubishi ML-21RS interface, without ROM.

With RS-232C rom in the computer

• Toshiba HX-20 (only the Japanese version)
• Toshiba HX-21
• Toshiba HX-23
• Toshiba HX-32
• Toshiba HX-33
• Toshiba HX-34

These computers are designed to be up-gradable with a kit version of the Toshiba HX-R700 interface:

• Toshiba HX-R701, kit version designed for the HX-20 (Japanese version), HX-21, HX-23 and HX-32 computers, I/O based
• Toshiba HX-R702, kit version designed for the HX-33 computer, I/O based
• Toshiba HX-R703, kit version designed for the HX-34 computer, I/O based

Stand-alone RS-232 interfaces

• ASCII MSX-Serial 232: BIOS v2.0, UART i8251 + i8253, DMA controller 82c37
• Digital Design DDX 80T: Integrated with 80 columns card, no standard BIOS (only a terminal emulator), unknown controller.
• Gradiente CT-80NET: BIOS v1.01, UART Z8530
• Harukaze Fast RS-232C: just the BIOS without MSX-BASIC support, UART 16550A - http://www.hat.hi-ho.ne.jp/tujikawa/ese/harukaze.html
• Kuma: no BIOS, I/O based
• Mitsubishi ML-20RS: no ROM
• Philips NMS 1210: no ROM, controlled by simulating ROM in RAM
• Philips NMS 1211: no ROM, controlled by simulating ROM in RAM
• Philips NMS 1212: no ROM, controlled by simulating ROM in RAM
• Pioneer PX-RS7: BIOS
• Repro Factory HBI-232MKII: BIOS v2.0, UART i8251 + i8253, I/O and memory (slot) based
• Sanyo MRS-001: BIOS, UART i8251 + i8253, I/O based
• Spectravideo SVI-757: BIOS
• Sony HBI-232: BIOS v2.0, UART i8251 + i8253, I/O and memory (slot) based, switch for terminal/modem operation
• Sunrise RS-232C: UART 16550A, lacks a BIOS
• Talent TRX-700:BIOS
• Talent TRX-710: BIOS
• Toshiba HX-R700: BIOS, UART i8251 + i8253, I/O based
• Victor IF-7610: BIOS, I/O based
• Yamaha Serial I/O Unit (MSX-NET): UART i8251 + i8253, side-slot module for Russian educational market (used in Yamaha YIS-503IIR)

Modems with integrated RS-232 interface

• Canon VM-300
• Daewoo CMD-120
• DCS Teltron 1200
• Digital Design DDX Modem
• Meisel V-3
• Micro Technology MT-Telcom
• Micro Technology MT-Telcom II
• Panasonic FS-CM1 (is also built in Panasonic FS-A1FM)
• Panasonic FS-CM820
• Philips NMS 1250 (no ROM)
• Philips NMS 1255 (no ROM)
• Sony HBI-300
• Sony HBI-1200 (is also built in Sony HB-T600 and Sony HB-T7)
• Spectravideo SVI-737
• Talent TLA-260
• Talent TLP-250
• Talent TMX-510
• Talent TMX-520
• The LINKS VIIK
• Toshiba Modem 300/300, 1200/75 (no ROM)

Non RS-232 interfaces

• Yamaha Serial I/O Unit Mk II (MSX-NET): UART YM3802, side-slot module for Russian educational market (MIDI based, used in Yamaha YIS-503IIIR and Yamaha YIS-805-128R2) - this module comes with a ROM containing Network BASIC.