NEC mPD780024AS Series Preliminary User's Manual page 255

(6) Program status word (PSW)
The program status word is a register to hold the instruction execution result and the current status for an interrupt
request. The IE flag to set maskable interrupt enable/disable and the ISP flag to control nesting processing are
mapped.
Besides 8-bit read/write, this register can carry out operations with a bit manipulation instruction and dedicated
instructions (EI and DI). When a vectored interrupt request is acknowledged, if the BRK instruction is executed,
the contents of PSW are automatically saved into a stack and the IE flag is reset to 0. If a maskable interrupt
request is acknowledged, the contents of the priority specification flag of the acknowledged interrupt are
transferred to the ISP flag. The PSW contents are also saved into the stack with the PUSH PSW instruction.
They are reset from the stack with the RETI, RETB, and POP PSW instructions.
RESET input sets PSW to 02H.
7 6 5
PSW IE Z RBS1
CHAPTER 15 INTERRUPT FUNCTIONS
Figure 15-7. Format of Program Status Word
4 3 2 1 0
AC RBS0 0 ISP CY
Preliminary User's Manual U16035EJ1V0UM
After reset
02H
Used when normal instruction is executed
ISP Priority of interrupt currently being serviced
0 High-priority interrupt servicing (Low-priority
interrupt disable)
Interrupt request not acknowledged, or low-
1
priority interrupt servicing (All maskable
interrupts enable)
IE Interrupt request acknowledge enable/disable
0 Disable
1
Enable
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