ST72561J9-Auto STMicroelectronics, ST72561J9-Auto Datasheet - Page 316

• Manufacturer Part Number: ST72561J9-Auto
• Description: 8-bit MCU for automotive
• Manufacturer: STMicroelectronics

Specifications of ST72561J9-Auto

• Hdflash Endurance: 100 cycles, data retention 20 years at 55 °C
• 5 Power Saving Modes: halt, auto wake up from halt, active halt, wait and slow

Important notes
24.1.3
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If these conditions are not met, the symptom can be avoided by implementing the following
sequence:
External interrupt missed
To avoid any risk of generating a parasitic interrupt, the edge detector is automatically
disabled for one clock cycle during an access to either DDR and OR. Any input signal edge
during this period will not be detected and will not generate an interrupt.
This case can typically occur if the application refreshes the port configuration registers at
intervals during runtime.
Workaround
The workaround is based on software checking the level on the interrupt pin before and after
writing to the PxOR or PxDDR registers. If there is a level change (depending on the
sensitivity programmed for this pin) the interrupt routine is invoked using the call instruction
with three extra PUSH instructions before executing the interrupt routine (this is to make the
call compatible with the IRET instruction at the end of the interrupt service routine).
But detection of the level change does ensure that edge occurs during the critical 1 cycle
duration and the interrupt has been missed. This may lead to occurrence of same interrupt
twice (one hardware and another with software call).
To avoid this, a semaphore is set to '1' before checking the level change. The semaphore is
changed to level '0' inside the interrupt routine. When a level change is detected, the
semaphore status is checked and if it is '1' this means that the last interrupt has been
missed. In this case, the interrupt routine is invoked with the call instruction.
There is another possible case, that is, if writing to PxOR or PxDDR is done with global
interrupts disabled (interrupt mask bit set). In this case, the semaphore is changed to '1'
when the level change is detected. Detecting a missed interrupt is done after the global
interrupts are enabled (interrupt mask bit reset) and by checking the status of the
semaphore. If it is '1' this means that the last interrupt was missed and the interrupt routine
is invoked with the call instruction.
To implement the workaround, the following software sequence is to be followed for writing
into the PxOR/PxDDR registers. The example is for Port PF1 with falling edge interrupt
sensitivity. The software sequence is given for both cases (global interrupt
disabled/enabled).
Case 1: writing to PxOR or PxDDR with global interrupts enabled:
LD A,#01
LD sema, A; set the semaphore to '1'
LD A, PFDR
AND A, #02
LD
LD A, #$90
LD PFDDR, A; write to PFDDR
LD A,#$ff
LD
PUSH CC
SIM
reset flag or interrupt mask
POP CC
X, A; store the level before writing to PxOR/PxDDR
PFOR, A ; write to PFOR
Doc ID 12370 Rev 8
ST72561-Auto