KS57C2308/P2308/C2316/P2316
ADDRESS SPACES
2-17
INTERRUPT STATUS FLAGS (IS0, IS1)
PSW bits IS0 and IS1 contain the current interrupt execution status values. You can manipulate IS0 and IS1
flags directly using 1-bit RAM control instructions
By manipulating interrupt status flags in conjunction with the interrupt priority register (IPR), you can process
multiple interrupts by anticipating the next interrupt in an execution sequence. The interrupt priority control circuit
determines the IS0 and IS1 settings in order to control multiple interrupt processing. When both interrupt status
flags are set to "0", all interrupts are allowed. The priority with which interrupts are processed is then determined
by the IPR.
When an interrupt occurs, IS0 and IS1 are pushed to the stack as part of the PSW and are automatically
incremented to the next higher priority level. Then, when the interrupt service routine ends with an IRET
instruction, IS0 and IS1 values are restored to the PSW. Table 2-6 shows the effects of IS0 and IS1 flag settings.
Table 2-6. Interrupt Status Flag Bit Settings
IS1
Value
IS0
Value
Status of Currently
Executing Process
Effect of IS0 and IS1 Settings
on Interrupt Request Control
0
0
0
All interrupt requests are serviced
0
1
1
Only high-priority interrupt(s) as determined in the
interrupt priority register (IPR) are serviced
1
0
2
No more interrupt requests are serviced
1
1
–
Not applicable; these bit settings are undefined
Since interrupt status flags can be addressed by write instructions, programs can exert direct control over
interrupt processing status. Before interrupt status flags can be addressed, however, you must first execute a DI
instruction to inhibit additional interrupt routines. When the bit manipulation has been completed, execute an EI
instruction to re-enable interrupt processing.
+
+
PROGRAMMING TIP — Setting ISx Flags for Interrupt Processing
The following instruction sequence shows how to use the IS0 and IS1 flags to control interrupt processing:
INTB
DI
; Disable interrupt
BITR
IS1
; IS1
←
0
BITS
IS0
; Allow interrupts according to IPR priority level
EI
; Enable interrupt
Summary of Contents for KS57C2308
Page 30: ...ADDRESS SPACES KS57C2308 P2308 C2316 P2316 2 22 NOTES ...
Page 168: ...SAM47 INSTRUCTION SET KS57C2308 P2308 C2316 P2316 5 94 NOTES ...
Page 170: ......
Page 206: ...POWER DOWN KS57C2308 P2308 C2316 P2316 8 8 NOTES ...
Page 210: ...RESET KS57C2308 P2308 C2316 P2316 9 4 NOTES ...
Page 222: ...I O PORTS KS57C2308 P2308 C2316 P2316 10 12 NOTES ...
Page 272: ...LCD CONTROLLER DRIVER KS57C2308 P2308 C2316 P2316 12 24 NOTES ...
Page 280: ...SERIAL I O INTERFACE KS57C2308 P2308 C2316 P2316 13 8 NOTES ...
Page 294: ...MECHANICAL DATA KS57C2308 P2308 C2316 P2316 15 2 NOTES ...
Page 310: ...KS57P2308 P2316 OTP KS57C2308 P2308 C2316 P2316 16 16 NOTES ...
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