NEC PD750008 - Manual (Page 42)

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µPD750008 USER'S MANUAL
SET1 MBE
CLR1 MBE
SET1 MBE
MBE
= 1
<Main program>
<Subroutine>
MBE
= 0
MEB
= 1
CLR1 MBE
MBE = 0
RET <Interrupt processing>
; MBE = 0 is to be set in the vector table.
MBE = 0
RETI
Internal hardware
and static RAM
operations are
repeated.
Applicable program processing Effect
MBE = 0 mode • Interrupt processing MBS save/restoration becomes unnecessary.
• Processing that repeats internal MBS modification becomes unnecessary.
hardware and static RAM operations
• Subroutine processing MBS save/restoration becomes
MBE = 1 mode • Usual program processing
Figure 3-1. Use of MBE = 0 Mode and MBE = 1 Mode
The contents of the MBE are automatically saved or restored at the time of subroutine processing, so that
the MBE can be freely modified during subroutine processing. In interrupt processing, the MBE is automatically
saved or restored, and when interrupt processing is started, the contents of the MBE can be specified for the
interrupt processing by setting the interrupt vector table. This speeds up interrupt processing.
The setting of the MBS can be modified for subroutine processing or interrupt processing by saving or
restoring the MBS with the PUSH or POP instruction.
The MBE is set using the SET1 or CLR1 instruction. The MBS is set using the SEL instruction.
Examples 1. The MBE is cleared, and a fixed memory bank is used.
CLR1 MBE ; MBE <– 0
2. Memory bank 1 is selected.
SET1 MBE ; MBE <– 1
SEL MB1 ; MBS <– 1