Difference between revisions of "84PCE:Ports:0020"
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0023-0025: Memory protection range upper limit (LSB in 23, MSB in 25) | 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 | + | Any memory access from unprivileged code at an address (after adding MBASE in z80 mode) in this inclusive range has the following effects: |
| − | * Reads | + | * Reads read-as-zero. |
* Writes don't affect the byte in memory and cause an nmi. | * Writes don't affect the byte in memory and cause an nmi. | ||
| + | * Privileged code can read and write normally. | ||
Revision as of 20:37, 26 August 2016
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 from unprivileged code at an address (after adding MBASE in z80 mode) in this inclusive range has the following effects:
- Reads read-as-zero.
- Writes don't affect the byte in memory and cause an nmi.
- Privileged code can read and write normally.
