84PCE:Ports:0020
From WikiTI
Synopsis
Port Number: 0020-0025
Function: Memory Protection Range
0020-0022: Memory protection range lower limit (LSB in 20, MSB in 22)
0023-0025: Memory protection range upper limit (LSB in 23, MSB in 25)
Any memory access at an address (after adding MBASE in z80 mode) in this (inclusive) range has the following effects:
- Reads always read-as-zero.
- Writes don't affect the byte in memory and cause an nmi.
