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||LK2||LK3||Language for BIOS messages|
|On||On||On||Diagnostic mode (English messages; most of the power on self test is skipped)|
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!)
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.
|Off||Off||Normal: Codepage 437|
|Off||On||Norwegian: Codepage 865|
|On||Off||Portugese: Codepage 860|
John Elliott 14 June 2003