Program Status Word Configuration - NEC PD78081(A) User Manual

(5) Program status word (PSW)
The program status word is a register to hold the instruction execution result and the current status for interrupt
request. The IE flag to set maskable interrupt enable/disable and the ISP flag to control multiple interrupt
processing are mapped.
Besides 8-bit unit 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 or when the BRK
instruction is executed, the contents of PSW is automatically saved to the stack and the IE flag is reset to 0.
If a maskable interrupt request is acknowledged the contents of the priority specify flag of the acknowledged
interrupt are transferred to the ISP flag. The contents of PSW are also saved to the stack by the PUSH PSW
instruction. It is reset from the stack with the RETI, RETB, and POP PSW instructions.
RESET input sets PSW to 02H.
7 6
PSW IE Z
180
CHAPTER 12 INTERRUPT FUNCTION
Figure 12-7. Program Status Word Configuration
5 4 3 2
RBS1 AC RBS0 0
State after
1 0
Reset
ISP CY 02H
Used when normal instruction is executed
ISP Priority of Interrupt Currently Being Received
0 High-priority interrupt servicing
(low-priority interrupt disable)
Interrupt not acknowledged or low-priority
interrupt request servicing
1
(all-maskable interrupts enable)
IE Interrupt Request Acknowledge Enable/Disable
0 Disable
1 Enable