Instruction manual

software OUT instructions to port 0 or port 1, respectively. This system is necessary because the Z80

computer executes code starting at 0x0000 when taken out of reset, so we need ROM there when the

computer starts. But, CP/M needs RAM in locations starting at 0x0000. Hence the need for the two

configurations.

The expansion board comes with a 2K EPROM with ROM code version 8 and above. It contains the

same monitor program and commands as the computer board ROM version 7, with additional

commands to read and write disk sectors, and to start CP/M. The version 8 ROM code lacks the simple

programs, such as the port reflector, that were present in ROM versions 7 and lower, that use the

computer board switches and LEDs for input and output. These computer board input and output ports

are disabled when the disk and memory expansion board is in use, as mentioned above. Removing the

code that used these ports allowed space for the extra version 8 commands and subroutines to be added.