NEC PD17062 User Manual
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148
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PD17062
12.5.1 Example of Using a Timer Based on a Timer Interrupt
An example follows.
Example
BR
AAA
; Branches to AAA.
TIMER:
; Program address 0003H
ADD
M1, #0001B ; Add 1 to M1.
SKT1
CY
; Tests the CY flag.
BR
BBB
; Returns if no carry is generated.
Process A
BBB:
EI
RETI
AAA:
INITFLG NOT BTM0ZX, NOT BTM0CK2, NOT BTM0CK1, NOT BTM0CK0
; Built-in macro
; Specifies the timer interrupt pulse as 5 ms.
MOV
M1, #0000B ; Clears the content of M1 to 0.
SET1
IPBTM0
; Enables a timer interrupt.
EI
; Enables all types of interrupts.
LOOP:
Process B
BR
LOOP
This program performs process A at every 80 ms.
At this point, note the following: Accepting an interrupt request causes a DI state automatically, and the
IRQBTM0 flag is set to 1 even in the DI state.
In other words, if process A takes 5 ms or longer, an interrupt request will be accepted immediately when
a return is made by a RETI instruction, thus disabling process B from being performed.