UPD784938 Datasheet, PDF (543/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 23 INTERRUPT FUNCTIONS
23.3.6 Program status word (PSW)
PSW is a register that holds the current status regarding instruction execution results and interrupt requests. The IE
flag that sets enabling/disabling of maskable interrupts is mapped in the low-order 8 bits of the PSW (PSWL).
PSWL can be read or written to with an 8-bit manipulation instruction, and can also be manipulated with a bit manipulation
instruction or dedicated instruction (EI/DI).
When a vectored interrupt is acknowledged or a BRK instruction is executed, PSWL is saved to the stack and the IE
flag is cleared (to 0). PSWL is also saved to the stack by the PUSH PSW instruction, and is restored from the stack by
the RETI, RETB and POP PSW instructions.
When context switching or a BRKCS instruction is executed, PSWL is saved to a fixed area in the register bank, and
the IE flag is cleared (to 0). PSWL is restored from the fixed area in the register bank by an RETCSI or RETCSB instruction.
RESET input clears PSWL to 00H.
7
PSWL S
Figure 23-6. Program Status Word (PSWL) Format
6
5
4
3
2
1
0
After reset
Z RSS AC
IE P/V
0
CY
00H
Used in normal instruction execution
IE
Interrupt Acknowledgment
Enabling/Disabling
0 Disabled
1 Enabled
Preliminary User’s Manual U13987EJ1V0UM00
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