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CHAPTER 21 INTERRUPT AND TEST FUNCTIONS
(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
processing are mapped.
In addition to being able to perform read and write operations in 8 bit units, operations using bit operation
commands and special commands (EI, DI) can be performed. Also, when a vectored interrupt request is
received or when a BRK command is executed, the contents of the PSW are automatically saved to the stack
and the IE flag is set at (0). Also, when a maskable interrupt request is received, the contents of the received
interrupt priority order specification flag are transferred to the ISP flag. The contents of the PSW are also saved
to the stack by the PUSH PSW command. The stack contents are recovered by the RETI, RETB and POP
PSW commands.
RESET input sets PSW to 02H.
Figure 21-9. Program Status Word Format
7
IEPSW
6
Z
5
RBS1
4
AC
3
RBS0
2
0
1
ISP
0
CY
02H
After
Reset
ISP
0
Used when normal instruction is executed
Priority of Interrupt Currently Being Received
High-priority interrupt servicing
(low-priority interrupt disable)
1
Interrupt request not acknowledged or low-priority
interrupt servicing
(all-maskable interrupts enable)
IE Interrupt request Acknowledge Enable/Disable
0 Disable
1 Enable