NEC uPD78P078 - Manual (Page 518)

518
CHAPTER 22 INTERRUPT FUNCTIONS
Figure 22-14. Interrupt Request Acknowledge Timing (Minimum Time)
Remark 1 clock: (f CPU : CPU clock)
Figure 22-15. Interrupt Request Acknowledge Timing (Maximum Time)
Remark 1 clock: (f
CPU
: CPU clock)
22.4.3 Software interrupt request acknowledge operation
A software interrupt request is acknowledged by BRK instruction execution. Software interrupt cannot be
disabled.
If a software interrupt is acknowledged, the contents of program status word (PSW) and program counter (PC)
are saved to stacks, in this order. Then the IE flag is reset (to 0), and the contents of the vector tables (003EH
and 003FH) are loaded into PC and branched.
Return from the software interrupt is possible with the RETB instruction.
Caution Do not use the RETI instruction for returning from the software interrupt.
f
CPU
1
Instruction Divide Instruction
PSW and PC Save,
Jump to Interrupt
Servicing
6 Clocks
Interrupt
Servicing
Program
33 Clocks
32 Clocks
CPU Processing
xxIF
(xxPR = 1)
xxIF
(xxPR = 0)
25 Clocks
f
CPU
1
Instruction Instruction
PSW and PC Save,
Jump to Interrupt
Servicing
6 Clocks
Interrupt
Servicing
Program
8 Clocks
7 Clocks
CPU Processing
xxIF
(xxPR = 1)
xxIF
(xxPR = 0)