Bios of Msx "1.5" machines

Expert (71)

29-08-2019, 01:38

I mean Msx 2 with 64 kb of vram: Toshiba HX-23, Canon V-25....

I wonder if they have a special bios that is able to handle 64 kb of vram only. Or are they equipped with the ordinary Msx 2 bios because it's already able to do that?

On Openmsx, HX-23 configuration file has this comment: "". HX-23F has 128 kb of vram. Unfortunatly i'm not able to test other "1.5" machines...

By snake

Expert (71)

29-08-2019, 01:45

The comment on HX-23 configuration file: "ROMs are assumed to be the same as HX-23F, which was used as a base for this config".
(sorry, it disappeared from the previous message because i pasted it with html comment delimiters)

By zeilemaker54

Champion (347)

29-08-2019, 05:31

MSX2 handles 64 KB VRAM, so same bios.

By zPasi

Champion (499)

29-08-2019, 07:24

I think MSX 1.5 usually means MSX1 with V9938 VDP, like SVI 738 X'press. MSX2 with 64 K VRAM is still MSX2.

By NYYRIKKI

Enlighted (6067)

29-08-2019, 08:23

Standard MSX2 BIOS detects the amount of VRAM on boot and if only 64kB is found it disables SCREEN 7 & SCREEN 8 usage and limits the usage of SET PAGE, COPY etc. The VRAM size information is stored in #FAFC

By sdsnatcher73

Prophet (3962)

29-08-2019, 15:04

And for the MSX1 machines with V9938. I don’t think they had a modified BIOS for the V9938 to work. It is basically backwards compatible with the TMS chips (if it were not MSX1 games would have issues on MSX2 computers).

By Grauw

Ascended (10768)

29-08-2019, 17:11

The Yamaha CX5MII has a modified BIOS, but it’s only for the memory mapper initialisation. They have a separate little ROM to support the V9938, it adds width 80 text mode support to MSX-BASIC 1.0 by attaching itself to various hooks. It doesn’t work in DOS(2) though, unfortunately.

By Nprod

Expert (102)

04-09-2019, 01:55

MSX2 is practically the same as MSX1 in terms of memory, just that most models have a memory mapper attached to a "slot" on the PCB layout itself. The standard definition for it only states a minimum of 64kb, it doesn't specify any requirement to have a mapper.