patc (05/12/82)
I need help with my Goubout System Support - I. I have a nearly full blown System Support - I board. There is one Ram chip in the ROM/RAM chip sockets addressed as global memory at 0F000H - 0FFFFH. My CPU is a Z-80 but has special circuitry to mirror I/O port addresses on the high address lines during IN and OUT instructions. If I address an I/O port in the range 0F0H to 0FFH, the system Support 1 enables the buss drivers for the data lines but does not select the RAM. This causes interference with the input/output data. When I modify the jumpers so an I/O address is not mirrored, it's even worse. The problem seems to depend on the type of IN/OUT instruction and the contents of the A or B register whether or not the board is enabled. Has anyone else encountered this problem? If so is there a fix for it. I do not use or need the battery backup for the RAM. Pat Caudill decvax!teklabs!tekmdp!patc ucbvax!teklabs!tekmdp!patc