HB-F1XD Japanese MSX2 - Replace V9938 with V9958?

Enlighted (6067)

11-09-2012, 00:22

Ok...

Now I have a new SUB-ROM for you!!!

I thought that it is very sad that you can't have boot logo when you have only 64KB ROM. This is because there is simply not enough space to put the logo to SUB-ROM. How ever it's typical for me to "reject your reality and substitute my own."

In MSX2 the boot logo is on SUB-ROM but in MSX2+ it did not fit anymore. Now I almost managed to squeeze it back in... Now you can use SET PASSWORD & SET TITLE commands and you can see the memory counter. How ever some things needed to go... This means the SET TITLE color parameter, the boot animation and the letters "M" & "S"...

How ever as a bonus feature I managed to squeeze in also a frequency selector so that you can boot to 50Hz mode if you hold down "H"-key until "beep".

See how your MSX will boot after the mods:
http://www.youtube.com/watch?v=agTKARNLQk8

~NYYRIKKI

By Colemu

Hero (542)

11-09-2012, 00:20

Thats is super cool

I have the only X model in existence!!

Superb work Nyyrikki - life saver.

Can't wait till I get started - MSX 2+ here I come......

By OeiOeiVogeltje

Paragon (1433)

11-09-2012, 18:30

me want sub-rom too?
for future maybe use

By RetroTechie

Paragon (1563)

11-09-2012, 19:15

NYYRIKKI wrote:

What I think is going on at the moment is that CE signal is connected to SLT0 and SLT30 signals trough OR-gate and A15 is connected to either SLT0 or SLT30. If you wish to add similar ROM as in HB-F1XDJ then you need to figure out how to connect rest of the SLT3X signals and also do new decoding for CE.

HB-F1XD service manual shows that ROM upper address (A14/15/16) and chip select lines come from a gate array (IC15, MB64H444), so it's anyone's guess how slot select signals relate to ROM A14/15/16 and CS signals.

Easiest would be to just unsolder it, put in an EPROM programmer that can be set to the correct pinout, and read the contents. Lacking a suitable programmer, you could even put the ROM in a breadboard, ground all lower address lines, set the upper ones manually by connecting to GND or +5V as needed, and then measure voltages on the D.. outputs (or connect LEDs to those). That way you could read the first byte(s) of each ROM block, and work out how blocks are organized. If Colemu is willing to send me the ROM chip, I could do that easily & upload ROM contents somewhere.

I suspect (but not sure!) using a 27C512 for replacement will be easy. Adding 2+ extension ROM by piggybacking a 27C256 is easy then. A single 1 Mbit EPROM is more elegant, but if it must include additional ROMs that aren't in the original machine, then it might be difficult to figure out how to control the upper address + chip select lines.

Either way, first thing is to dump exact contents of original ROM. @Colemu: if there's room on the board for it, do yourself a favor & solder in a 32 pin socket even if you intend to put the original ROM back in (or a 27C512). Modifying a few pins on a socket is easy; later on replacing a 28 pin with a 32 pin socket is annoying, unnecessary work.

By Colemu

Hero (542)

11-09-2012, 20:05

I will remove the rom and read the contents before I move on to the next step. It may give us an idea what the best next step will be.

By Colemu

Hero (542)

11-09-2012, 23:34

Alright I desoldered the Basic rom. Can you advise what settings to use on the programmer to read this chip??

I have space to add a 32 pin socket in the board. I only have 28 pin sockets at hand however.

My programmer is a standard Willem

UPDATE: I think I've managed to read at least the 1st 64k of the Rom

By RetroTechie

Paragon (1563)

12-09-2012, 00:06

Pinout for that ROM is almost identical to a 27(C)512 EPROM, only where ROM has highest address line (A16) the EPROM has /Output Enable, which has to be low to read data. So if you read it as if it were a 27512, you should get lower half of the 128 KB.

Note that some EPROMs can identify themselves by putting a higher voltage on one of the address lines, this should not even be tried with that ROM as it would kill it! So I'd check first to make sure that Willem programmer won't do that. And of course don't try any programming actions (duh)...

Colemu wrote:

UPDATE: I think I've managed to read at least the 1st 64k of the Rom

Ah right, so 27512 EPROM setting, eh? Can you post the contents of that 64KB you read? It should be easy to identify what's what in there.

P.S. you could read other half by bending that pin (22, see a 27512 datasheet if you're not sure how pins are numbered) sideways before placing it in EPROM programmer socket. Solder a wire from that pin to pin 28 (= +5V) so it's at logic high while in the Willem programmer. Then when read out like a 27512, you get the upper half. If you can: post that too, please?

By RetroTechie

Paragon (1563)

12-09-2012, 00:11

Colemu wrote:

I have space to add a 32 pin socket in the board. I only have 28 pin sockets at hand however.

With a knife you could butcher a 28 pin socket to add the remaining 4 contacts. Still easier to grab a 32 pin socket though.

By Colemu

Hero (542)

12-09-2012, 00:25

I've had a look at the first 64k and the Main rom is first, followed by the Sub, followed by the Disk (I checked it against the individual openMSX roms. It looks like there is just empty space after, so I recon that the second half of the rom is empty.
How do I post the rom for you to see?

I've sent a message, can you reply? Then I'll attach the file for you...

By RetroTechie

Paragon (1563)

12-09-2012, 00:55

Where "Main rom" = 32KB, you mean? In that case, if there's no other ROM blocks used in the machine (KUN compiler for example), a 27(C)512 EPROM would be a drop-in replacement.

What's /Output Enable for the ROM, is /Chip Enable for the EPROM. Both must be active (low) to output data. /Output Enable for the EPROM is A16 for the ROM, so a 27C512 would output data whenever a lower half address of the ROM is read. When an upper half location is read, A16 = high would work as output disable for the 27C512, so you'd read FFh, like a 128 KB ROM with empty upper half. Hardware-wise, no problem.