lalakobe wrote on 2020-06-21, 15:37:
Hi all! […]
I want to assemble a 286 machine and I need some advice from you guys.
What 286 motherboards are considered better than others? What models should I look for?
AFAIK there were motherboards with SIMM slots, were they more or less common? Should I try to buy one?
Were there models with CR-2032 CMOS batteries or they all required 4.5v at these times?
Thanks in advance!
I'm not an expert myself on 286 motherboards or which chipsets are considered to be the best.
Some chipsets that come to mind are Headland's HT12 & GC101A-PC chipsets, VLSI's VL82C10x , UMC's UM82C206 & Suntac's ST62c2xx chipsets.
Some of the later motherboards had CPU's from AMD & Harris that went up to 20 MHz (Harris also made a 25 MHz CPU), so you have to decide what CPU speed you're after. The most common ones that I've seen are mostly 12 MHz CPU's.
Yes, there were later 286 motherboards that did have simm sockets (my Suntac J-286P motherboard has simm sockets, in combination with some DRAM sockets). There were slightly older 286 motherboards that used SIPP memory (which are electrically compatible with 30-pin simms), but finding SIPPs these days are almost impossible. You can, however, convert a simm into a SIPP or, just remove the SIPP sockets on the motherboard and solder on 30-pin simm sockets (from a donor motherboard).
I would simply just connect an external battery pack to the motherboard (almost all the motherboards from that era had external battery headers). Just remember that a CR-2032 is not supposed to be charged, but you can place a diode in between if the circuit is trying to charge the battery. However, older motherboards (like your 286 & 386 motherboards) normally required at least 4.5V when connecting an external battery pack (due to the diode that reduces the voltage output). You will most likely find that a 3V CR-2032 will not provide sufficient voltage to keep all the settings in the BIOS . You can safely even connect a 6V external battery pack to the motherboard (some 286 manuals even specifically mention this).