ST92F124/F150/F250 - INTERRUPTS
WAKE-UP / INTERRUPT LINES MANAGEMENT UNIT (Cont’d)
5.12.3.4 NMI Pin Management
– If the ST9 is in Run mode and a rising edge oc-
curs on the NMI pin: the NMI service routine is
executed and then the ST9 restarts the execu-
tion of the main program. Now, suppose that
the user wants to enter STOP mode with NMI
still at 1. The ST9 will not enter STOP mode
and it will not execute an NMI routine be-
cause there were no transitions on the exter-
nal NMI line.
On the CPU side, if TLTEV=1 (Top Level Trigger
Event, bit 3 of register R246, page 0) then a rising
edge on the NMI pin will set the TLIP bit (Top Level
Interrupt Pending bit, R230.6). At this point an in-
terrupt request to the CPU is given either if TL-
NM=1 (Top Level Not Maskable bit, R247.7 - once
set it can only be cleared by RESET) or if TLI=1
and IEN=1 (bits R230.5, R230.4).
– If the ST9 is in run mode and a rising edge on
NMI pin occurs during the STOP bit setting se-
quence: the NMI interrupt will be acknowledged
and the ST9 will not enter STOP mode. At the
end of the NMI routine, the user must re-enter
the sequence: if NMI is still high at the end of the
sequence, the ST9 can not enter STOP mode
(see previous case).
Assuming that the application uses a non-maska-
ble Top Level Interrupt (TLNM=1): in this case,
whenever a rising edge occurs on the NMI pin, the
related service routine will be executed. To service
further Top Level Interrupt Requests, it is neces-
sary to generate a new rising edge on the external
NMI pin.
The following summarizes some typical cases:
– If the ST9 is in run mode and the NMI pin is high:
if NMI is forced low just before the third write in-
struction of the STOP bit setting sequence then
the ST9 will enter STOP mode.
– If the ST9 is in STOP mode and a rising edge on
the NMI pin occurs, the ST9 will exit STOP
mode and the NMI service routine will be exe-
cuted.
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STMICROELECTRONICS [ ST ]
