The ZX96' bus is similar to the ZX81' bus, i.e. the data bus is decoupled from the CPU by 470 Ohm resistors. With only a few extension boards supplied it should work without a driver too, but a complete upgraded ZX96 will bore you with a lot of crashes then. Anyway, a driver board is necessary for a reliable system.

The driver board buffers the whole data- and adressbus and the usual needed control lines. As there is usually memory at the ZX96 board, the data bus driver normally must be disabled. Only when data transfer is required from/to any extension board this board must set /BUSCS=low, thus activating the driver. And, for displaying any HRG (HiResolutionGraphics) that is stored in memory 'behind' the drivers, the data bus must be directed to the CPU in RFSH cycle too.

Kai Fischer, ZX-TEAM

last updated Mar/00