Switchable I/O ports
When a value is written to the register 40h, this allows to access to the corresponding device(s) via ports 41h~4Fh. The value is an ID to select the device(s).
Here are the reserved or used IDs so far:
| ID | Devices |
|---|---|
| 1 | ASCII/Microsoft |
| 2 | Canon |
| 3 | Casio |
| 4 | Fujitsu |
| 5 | General |
| 6 | Hitachi |
| 7 | Kyocera |
| 8 | Matsushita (Used for MSX2+) |
| 9 | Mitsubishi |
| 10 | NEC |
| 11 | Yamaha |
| 12 | JVC |
| 13 | Philips |
| 14 | Pioneer |
| 15 | Sanyo |
| 16 | Sharp |
| 17 | SONY |
| 18 | Spectravideo |
| 19 | Toshiba |
| 20 | Mitsumi |
| 21 | Telematica |
| 22 | Gradiente |
| 23 | Sharp Brazil |
| 24 | GoldStar (LG) |
| 25 | Daewoo |
| 26 | Samsung |
| 128 | Matsushita's Image Scanner |
| 165 | WORP3 |
| 170 | SuperSoniqs's Darky |
| 171 | SuperSoniqs's Darky second setting |
| 212 | 1chipMSX / Zemmix Neo (KdL firmware) |
| 254 | ASCII's MPS2 |
ID numbers between 1 and 127 are ID numbers for MSX manufacturers for built-in devices, and ID numbers 128 to 254 are for external devices.
Writing 0 (or an unused value) to port 40h disables extended I/O ports.
Example of use with Panasonic MSX2+:
- Write value 8 at port 40h to enable extended I/O ports for Panasonic MSX2+.
- Read the port 040h. If the value read is 247, it is that it is a Panasonic MSX2+ having a Z80 with turbo mode (5.37MHz).
- You can therefore write 0 to port 41h to activate turbo mode or 1 to deactivate it. Reading bit 0 of this port will tell you the current mode and bit 7 will show you the internal software switch state (0 for Off).