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CHAPTER 16 INTERRUPT FUNCTION
User
’
s Manual U15017EJ2V0UD
Cautions 1.
Macro service requests are acknowledged and serviced even during execution of a non-
maskable interrupt service program. If you do not want macro service processing to be
performed during a non-maskable interrupt service program, you should manipulate the
interrupt mask register in the non-maskable interrupt service program to prevent macro
service generation.
The RETI instruction must be used to return from a non-maskable interrupt. Subsequent
interrupt acknowledgment will not be performed normally if a different instruction is used.
If you restart a program from the initial state after a non-maskable interrupt acknowledgment,
refer to 16.12 Restoring Interrupt Function to Initial State.
Non-maskable interrupts are always acknowledged, except during non-maskable interrupt
service program execution (except when a high non-maskable interrupt request is generated
during execution of a low-priority non-maskable interrupt service program) and for a certain
period after execution of the special instructions shown in 16.9. Therefore, a non-maskable
interrupt will be acknowledged even when the stack pointer (SP) value is undefined, in
particular after reset release, etc. In this case, depending on the value of the SP, it may
happen that the program counter (PC) and program status word (PSW) are written to the
address of a write-inhibited special function register (SFR) (refer to Table 3-6 in 3.8 Special
Function Registers (SFRs)), and the CPU becomes deadlocked, or an unexpected signal is
output from a pin, or the PC and PSW are written to an address in which RAM is not mounted,
with the result that the return from the non-maskable interrupt service program is not
performed normally and a software inadvertently loops.
Therefore, the program after RESET release must be as shown below.
2.
3.
CSEG AT 0
DW
STRT
CSEG BASE
STRT:
LOCATION 0FH; or LOCATION 0H
MOVG SP, #imm24