86:Ports:05

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.