NEC 78014Y Series, User Manual

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CHAPTER 18 INTERRUPT FUNCTIONS AND TEST FUNCTION
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(6) 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 servicing
are mapped.
Besides 8-bit units 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, and when the BRK
instruction is executed, the contents of PSW is 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 specify flag of the acknowledged
interrupt are transferred to the ISP flag. The contents of acknowledged interrupt is also saved into the stack with
the PUSH PSW instruction. It is reset from the stack with the RETI, RETB and POP PSW instructions.
RESET input sets PSW to 02H.
Figure 18-8. Program Status Word Configuration
Symbol 7 6 5 4 3 2 1 0 When Reset
PSW IE Z RBS1 AC RBS0 0 ISP CY 02H
Use when normal instruction is executed
ISP Priority of Interrupt Currently Being Serviced
0 High-priority interrupt servicing (low-priority
interrupt disable)
1 Interrupt request not acknowledged or low
priority servicing (all maskable interrupts
enable)
IE Interrupt Request Acknowledge Enable/Disable
0 Disable
1 Enable