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RL78/G1A CHAPTER 16 INTERRUPT FUNCTIONS
16.3.5 Program status word (PSW)
<R>
The program status word is a register used to hold the instruction execution result and the current status for an interrupt
request. The IE flag that sets maskable interrupt enable/disable and the ISP0 and ISP1 flags that controls multiple
interrupt servicing are mapped to the PSW.
Besides 8-bit read/write, this register can carry out operations using bit manipulation instructions and dedicated
instructions (EI and DI). When a vectored interrupt request is acknowledged, if the BRK instruction is executed, the
contents of the 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 register of the acknowledged interrupt are not 00, its value
minus 1 is transferred to the ISP0 and ISP1 flags. The PSW contents are also saved into the stack with the PUSH PSW
instruction. They are restored from the stack with the RETI, RETB, and POP PSW instructions.
Reset signal generation sets PSW to 06H.
Figure 16-6. Configuration of Program Status Word
<7>
IE
<6>
Z
<5>
RBS1
<4>
AC
<3>
RBS0
<2>
ISP1
<1>
ISP0
0
CYPSW
After reset
06H
ISP1
0
0
1
1
Enables interrupt of level 0
(while interrupt of level 1 or 0 is being serviced).
Enables interrupt of level 0 and 1
(while interrupt of level 2 is being serviced).
Enables interrupt of level 0 to 2
(while interrupt of level 3 is being serviced).
Enables all interrupts
(waits for acknowledgment of an interrupt).
Jul 04, 2013
IE
0
1
Disabled
Enabled
Priority of interrupt currently being serviced
Interrupt request acknowledgment enable/disable
Used when normal instruction is executed
ISP0
0
1
0
1
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