GuillermoXT wrote on 2021-04-02, 13:10:

I have a 48mhz oscillator in my 286 but the clock is only adjustable between 6 and 8MHz.
Do I have a divider bigger than 2?

Yes probably.
48/6=8 and 48/8=6 😀

waterbeesje wrote on 2021-04-02, 14:05:

GuillermoXT wrote on 2021-04-02, 13:10:

I have a 48mhz oscillator in my 286 but the clock is only adjustable between 6 and 8MHz.
Do I have a divider bigger than 2?

Yes probably.
48/6=8 and 48/8=6 😀

Is there any possibility to "tell" the Bios that it should set the divider to 4 for example?
I exchanged the original 8mhz Cpu with a 12Mhz in that Tandon board.
There are no jumpers and the 8 dip switches i figured out are only for the memory settings.

GuillermoXT wrote on 2021-04-02, 14:27:

Is there any possibility to "tell" the Bios that it should set the divider to 4 for example? I exchanged the original 8mhz Cpu w […]
Show full quote

waterbeesje wrote on 2021-04-02, 14:05:

GuillermoXT wrote on 2021-04-02, 13:10:

I have a 48mhz oscillator in my 286 but the clock is only adjustable between 6 and 8MHz.
Do I have a divider bigger than 2?

Yes probably.
48/6=8 and 48/8=6 😀

Is there any possibility to "tell" the Bios that it should set the divider to 4 for example?
I exchanged the original 8mhz Cpu with a 12Mhz in that Tandon board.
There are no jumpers and the 8 dip switches i figured out are only for the memory settings.

15958781994551097950550545440254.jpg

With an early board like this, there's a lot more to take in account.
Like what sled the other components are capable of.

But to solve this, it might be a good idea to start your own thread, rather than posting in a thread for a totally different board 😀

Split posts to new thread.

waterbeesje wrote on 2021-04-02, 16:42:

With an early board like this, there's a lot more to take in account. Like what sled the other components are capable of. […]
Show full quote

GuillermoXT wrote on 2021-04-02, 14:27:

Is there any possibility to "tell" the Bios that it should set the divider to 4 for example? I exchanged the original 8mhz Cpu w […]
Show full quote

waterbeesje wrote on 2021-04-02, 14:05:

Yes probably.
48/6=8 and 48/8=6 😀

Is there any possibility to "tell" the Bios that it should set the divider to 4 for example?
I exchanged the original 8mhz Cpu with a 12Mhz in that Tandon board.
There are no jumpers and the 8 dip switches i figured out are only for the memory settings.

15958781994551097950550545440254.jpg

With an early board like this, there's a lot more to take in account.
Like what sled the other components are capable of.

But to solve this, it might be a good idea to start your own thread, rather than posting in a thread for a totally different board 😀

Agree waterbeesje !
6Mhz non turbo and 8Mhz Turbo speed ?
And no on the BIOS setting the divider on a 286 (have never seen one), that would be set by jumpers or switches if there are any for that purpose.
Most 286 boards support only a one or two main clock/crystal frequencies by design and have dividers set so ISA bus does not exceed 8Mhz if they allow different clock speeds.
So in general most 8Mhz 286, 12Mhz 286 and 16Mhz 286 run only at those design speeds and only have a turbo/de-turbo switch to lower them to 6 or 8Mhz (depending on the board) or run full speed.

In my case I suppose the turbo switch is my bios setting between 6 & 8MHz? What if I swap the 48mhz oscillator for a higher clocked one?

Then you mess with the ISA bus and memory timing if all clocked off the crystal (most XT, 286 and 386 are). At 48Mhz is probably 8Mhz to ISA (48K/6=8Mhz). Many ISA cards have issues above 9Mhz so best is 54Mhz Xtal which will be 9Mhz cpu.
At 12Mhz cpu clock would require 72Mhz Xtal/clock and put the ISA at 12Mhz also....not good !
Can you post a picture of your board ?
Most XT, 286 and 386 are not designed for changing clocks much....

Horun wrote on 2021-04-03, 02:33:

Then you mess with the ISA bus and memory timing if all clocked off the crystal (most XT, 286 and 386 are). At 48Mhz is probably […]
Show full quote

Then you mess with the ISA bus and memory timing if all clocked off the crystal (most XT, 286 and 386 are). At 48Mhz is probably 8Mhz to ISA (48K/6=8Mhz). Many ISA cards have issues above 9Mhz so best is 54Mhz Xtal which will be 9Mhz cpu.
At 12Mhz cpu clock would require 72Mhz Xtal/clock and put the ISA at 12Mhz also....not good !
Can you post a picture of your board ?
Most XT, 286 and 386 are not designed for changing clocks much....

This is my Board
I remember that there existed a 10MHz version and i think that the difference may come from a different divider set by the Bios? 🤔
Could it be possible to build an own clock Generator for the CPU so the ISA Bus can run at its standard speed?
I swapped the 8Mhz for a 10MHz Cpu and added a 287 10MHz meanwhile

my first PC was an XT, running at 10MHz. The bloody thing kept crashing in windows, shop couldn't figure out why.
After some reading and reasoning it became clear, the serial port card to which the mouse was connected couldn't handle the 10MHz ISA bus.
pretty f'n annoying at the time.

Stiletto wrote on 2021-04-02, 22:58:

Split posts to new thread.

Thanks very much 🙂👍

Don't do what I did with ibm AT motherboard (was given to me) back in the day and tried to sped it up and it died in the process of overclocking. From 6 to 8 even 10MHz. Reason, that thing had replaceable crystal.

Cheers,

Ok so i will continue searching for a 286highend or 386/486 👍

By the way I have a 3mb xms card installed is there a way to tell DOS to use it as usable memory?

If it is a XMS only card then you need XMA2EMS.SYS from MS DOS 4 (or XMAEM.SYS from IBM PC-DOS 4) to convert to EMS to use it as Expanded RAM. It might needs some specific driver.
What brand and model is the memory card ?

Horun wrote on 2021-04-04, 15:08:

If it is a XMS only card then you need XMA2EMS.SYS from MS DOS 4 (or XMAEM.SYS from IBM PC-DOS 4) to convert to EMS to use it as Expanded RAM. It might needs some specific driver.
What brand and model is the memory card ?

Someone told me it was usually for a Nixdorf 8810 but my bios recognize it and adds the 3mb to the 1mb system memory to a total of 4MB at boot up.

now that's a big ISA card...

I like it!

If the system already recognises the ram at post, it's probably going to work well with himem.sys to get xms. For EMS you could load the xma2ems as Horun said. Or maybe there's some BIOS switch to set EMS/xms?