Hi everybody, i am new here and ready to ask my first question.

I bought a secondhand 8250 and it has two switches on the front that are normaly not there. I figured out that one is for turning the build in dos2 eprom on/off. The other one i cant figure out, may be it is a 7 mhz switch?

How can i find out wat this switch does?

Thnx,

Xull

let's list a few possible functions:

• MSX-DOS 2
  
• Turbo 7MHz
  
• MSX 2+
  
• Memory (though, switchable between 128 KB and what's in there is kinda weird)
  
• VRAM (same here)
  
• Some added built-in program (like KUN-BASIC compiler ROM, try CALL BC and see if it works)
  
• Fast diskrom (again, strange to put that on a switch)
  

Hope this helps.

Ok thnx, i try the kun basic thing....

Yeah well.....And how to test it......Try to boot MSXDOS2 with a floppydisk where you have copied COMMAND2.COM and MSXDOS2.SYS onto.....Or make a little Basic program which for example puts a counter on the screen, turn over the switch and see if the counting goes faster Then it's the 7mhz switch

I already indentified the first button to be msx-dos 2, because the system told me there was a version 2.xx of disk basic. And also booting with command2.com and msxdos2.sys worked.
I will try the counter program.

On startup, the computer says it has 1024 kbytes of ram. This is done by putting something in a eprom, right?

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On startup, the computer says it has 1024 kbytes of ram. This is done by putting something in a eprom, right?

The eprom containing the MSX2 extended rom or sub-rom contains a routine that counts the memory size and displays that on the screen in the startup screen.

Does it? On the turboR it works even with external memory. On MSX it doesn't.

MSX2+ and up count total internal and external memory. MSX2 and down do not count anything. An MSX2 printing something different than standard has a modified BIOS rom.
I have a NMS8250 with a switch and 2 LEDs to switch between a Philips and Sony diskrom (at least that's what I've been told).

I didn't say that the memory counter in MSX2 is a standard feature. I know it is with the MSX2+ and MSXturboR. Where do you think the counter code came from initially?

There were/are modified roms available where the counter code is added.

I have opened my 8250 and found out that the other switch is a 7 mhz on/off switch. There is a little pcb with a xtal on top of the z80.
Also the basic programs run faster and the music (psg) sounds grinded(?)...

Thnx for your help!

Yeah the sounds doubles in frequency. The PSG uses the Z80 frequency as base. However, because the VDP can't handle a 7.16MHz Z80, it is slowed down to 3.58MHz during VDP accesses. That's why the PSG sounds more garbled than just doubled.

BiFi...

Quote:

Fast diskrom (again, strange to put that on a switch)

not so strange, my sony can switch between a fast HPN diskROM and a slower but better MCWF diskROM. xmpl: XAK doesnt feel confident using the HPN diskROM.

actually, switching between more and less RAM seems useless to me, however, switching between 128Kb and 192Kb VRAM can be usefull! Certain software seems to be
unconfortable with more VRAM (reason unknown to me).
I remember Jarretenk having problems maintaining a perfect screensplit when using 192Kb VRAM instead of 128KB.