PC200 motherboard links

The Sinclair PC200 motherboard has 7 option links. Some of them have jumper pins already present; others would need the jumpers soldered on to be used.

LK1-LK3: Language

LK4: Memory size

This link has a jumper on three pins. If it is on the left-hand pair of pins, then the memory size is 512k. If it is on the right-hand pair, the memory size is 640k (the extra memory chips must actually be present on the motherboard!)

LK5: Unknown

According to the service manual, this link has three pins: Ground, +5 Volts, and the NDMACS line (which runs between the bus gate array and the DMA controller). There are three possible uses for this:

• To pull NDMACS permanently low or high. Perhaps this disables the DMA controller so that an alternative can be used.
• For testing the DMA controller or the bus gate array.
• To support a peripheral which needs these signals.

LK6,7: Builtin graphics adaptor fonts

Unlike the other links, these can be seen simply by opening the expansion bay cover; there is a hole in the motherboard shielding which exposes these links and a ROM chip which contains the fonts.

The links affect the built-in MDA and CGA fonts.