Philips VG 8235 DS Disk Rom?

By grit

Resident (53)

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24-11-2014, 16:40

I was wondering, to replace a disk rom to the VG8235, could I drop in a diskrom from the NSM8245? It looks like they have the same controller? (ofcourse I'm changing the drive too)

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By Jipe

Paragon (1365)

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24-11-2014, 18:03

yes is possible but exist many models of VG8235
see serial number under the MSX
/00/02/19 have a 16k Diskrom
/20/22/29/36/39 have a 64k rom with 16k for Diskrom

By grit

Resident (53)

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24-11-2014, 18:32

Thanks Jipe, I see I have the /20 - I was already glad they put in a socket under the diskrom. Did they combine roms on the /20 version ?

I am able to burn eproms but am not sure what has to go where.

By grit

Resident (53)

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24-11-2014, 18:56

hmm, dumped the rom to monitor and it looks like this:

0000 -7FFF - MSX ROM
8000-BFFF - MSX2 ROM
C000--FFFF - Disk ROM

so it seems I just have to overwrite C000-FFFF with the new diskrom

By grit

Resident (53)

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24-11-2014, 22:49

Well, that all worked out, I can do CALL FORMAT and I have the single / double sided option

but... I get 'disk offline' all the time. Now here are my findings:

I used these references:
page 13 of the service manual:
http://msx.hansotten.com/uploads/msxdocs/vg8235sm20.pdf
the drive conversion pdf:
http://msx.hansotten.com/uploads/msxdocs/floppypcmsx.pdf
and:
http://www.bas-ditta.info/verkoopenlinks/doehetzelf/diskdriv...

Hans Otten's description has some extra info on the PC-drive connector but uses some adapter I don't have. The Bas-Ditta page has detailed description about adjusting the cable. I put it together a bit:

Drive cable pinout of the VG-8235:
VG8235             FLOPPY DRIVE
1  /ip          -  8  (index)
2  /dir         -  18 (direction)
3  /step      	-  20 (step)
4  /wd		-  22 (write data)
5  /wg		-  24 (write gate)
6  /ds0		-  10 (select 0)
7  /ds1		-  12 (select 1)
8  /ds2		-  14 (select 2)
9  /ds3		-  6  (select 3)
10 /motr on	-  16 (motor on)

11 gnd		-  *  (ground it - seperate thicker cable on the connector)

12 /tr00      	-  26 (track00)
13 /wp		-  28 (write protect)
14 /rd		-  30 (read data)

Double checked this and the pins seem to work out.

There's only a vague mention of adjusting the PC drive to DS0 and the RDY signal.
I have this drive: Mitsumi D359T3 And it seems on Amiga's you have to do the same kind of trick to use a PC drive in the computer. I found this adaptation:
http://www.pitsch.de/stuff/amiga/mitsumid359t3_done.jpg

And put it together with these jumper settings:
http://embeddedsw.net/EMUFDD_MITSUMI_Jumpers.html
As the bottom of the PCB states it should be something like this

Seems ok doesn't it? Any ideas why I get the disk offline? Calling 'FILES' commmand does spin the drive. Drive LED on the top of the MSX lights up but not the led on the disk itself. The drive works - I had it on my PC earlier.

I'm powering the drive from an external PC PSU but ground the pin 11 from the VG8235 connector to the floppy drive as well.

By Jipe

Paragon (1365)

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25-11-2014, 15:32

missing the SIDE SELECT signal , you can inspire to this mod
http://www.msxvillage.fr/articles/?url=/2-bricolage/60-lecte...

By Guts

Expert (87)

Guts's picture

25-11-2014, 19:55

2 weeks ago I do the same mod on my VG-8235, I use a 16k disk rom and I take the guide from Bas-Ditta.
But I use a pin header as connector for my floppy drive.

Works really great Wink

By roadfighter

Champion (380)

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25-11-2014, 21:39

Jipe wrote:

missing the SIDE SELECT signal , you can ..............

If you are using the mod from Bas then it also has a Side select signal.
His modification works just fine.

Emil

By grit

Resident (53)

grit's picture

26-11-2014, 09:06

I put together my own rom with the bios from the original 8235 and the diskrom part from the 8245 (I have the 64K maskrom type 8235). Not sure if there's something changed in Bas' rom to fake that signal but I'm still getting nothing. Thanks for the msxvillage link by the way - hadn't seen that one. I also wired those two signals from the B-connector. I saw this description on Hans Otten's page but was not sure what he meant with 'B-Connector'

Tried FILES "b:" as well but also disk-offline there...