Difference between revisions of "86:Ports:05"
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'''Function:''' Lower Memory Bank Port | '''Function:''' Lower Memory Bank Port | ||
| − | This port controls which memory bank is accessible in the 4000-7FFFh range. See [[86 | + | This port controls which memory bank is accessible in the 4000-7FFFh range. See [[86:Memory_Mapping|Memory Mapping]] for the interpretation of the banks & pages. |
=== Read Values === | === Read Values === | ||
Latest revision as of 01:07, 20 September 2021
Synopsis
Port Number: 05h
Function: Lower Memory Bank Port
This port controls which memory bank is accessible in the 4000-7FFFh range. See Memory Mapping for the interpretation of the banks & pages.
Read Values
- Bit 0-7: Reads last value written.
Write Values
- Bit 0-5: Page select (external address bits 14-19).
- Bit 6-7: Bank select.
Comments
- This port is set to 0Dh when the OS passes control to a program.
- Set this port to 0Dh before attempting to call OS functions, because that page contains the public ROM call table. Also be sure to set it to 0Dh before returning to the OS.
