Philips 8250 v 8255

By caver99

Rookie (22)

caver99's picture

30-08-2009, 21:59

Could some one tell me the differences between the 2 above..
What is involved in turning an 8250 into an msx2+

What is this about 7mhz on an 8250, is it worth doing if so is there any info regarding this mod
plus i am now on the lookout for a 4mb 30pin simm to do a 4mb ram upgrade for symbios plus hdd of some sort.

Regards

Graham

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By OeiOeiVogeltje

Paragon (1406)

OeiOeiVogeltje's picture

30-08-2009, 22:25

nothing
the 8255 has a second floppydrive
thats it

By dhau

Paragon (1570)

dhau's picture

30-08-2009, 23:00

4MB 30-pin SIMMs are relatively exotic, eBay is probably the best source (those where in demand in mid-90s for SB AWE and GUS PnP). 1MB SIMMs can be bought for roughly 1$ per kilo Smile On MSX imo anything above 512K is only useful for symbos and may be uzix, so 1MB is a lot.

7MHz mod is all about cutting clock output from VDP and putting it though some sort of turbo diy schematic, main function being synching singal fronts between original signal and a new doubled signal, so computer won't hang during freq switch. Speed is reverted to original every time there is bus request of any sort, so doubling frequency doesn't really double speed, like in PCs.

VDP mod requires removal of 9938, adding socket, rerouting several pins, adding register schematics, as well as replacing bios roms with MSX2+ compatible.

Hans Otten hosts information about those mods.

By caver99

Rookie (22)

caver99's picture

31-08-2009, 00:15

cool, i was hoping to run symbos on the ms2 plus found an artical about putting disk os on rom internaly, cant wait till i get the 8250, Thanks, i will be on here even more now