As originally aimed, TTL etc is not used with 3 chip configuration.
Access range of external memory
It is better to access all 64 KB spaces from PIC, but since the mandatory condition for launching CP / M is to access only the first and last areas of the memory area, the memory access range from PIC is
I am using HALT, and I use RESET rather than NMI (INT) to escape HALT in order to reduce the number of PIC's I/O pins. Please see URL below for details.
External crystal is also unnecessary because the clock of the transmitter built in PIC is supplied to Z80 (Z80 operates at 16 MHz).
The switch input port is also used as the LED control port.