UPD17708 datasheet(295/356 Pages) NEC

295 / 356 page

295

µPD17704, 17705, 17707, 17708, 17709

20.2.5 Releasing halt status by basic timer 0 carry FF

Releasing the halt status by using the basic timer 0 carry FF is specified by the “HALT 0010B” instruction.

When releasing the halt status by the basic timer 0 carry FF is specified, the halt status is released as soon as

the basic timer 0 carry FF has been set to 1.

The basic timer 0 carry FF corresponds to the BTM0CY flag on a one-to-one basis and is set at fixed time intervals

(100, 50, 20, or 10 ms). Therefore, the halt status can be released at fixed time intervals.

Example To release halt status every 100 ms to execute processing A

HLTTMR

DAT

0010B

; Symbol definition

INITFLG

NOT BTM0CK1, NOT BTM0CK0 ; Sets time interval of basic timer 0 to 100 ms

LOOP:

HALT

HLTTMR

; Specifies setting of basic timer 0 carry FF as halt releasing condition

SKT1

BTMOCY

; Embedded macro

LOOP

; Branches to LOOP if BTM0CY flag is not set

Processing A

; Executes processing A if carry occurs

LOOP

20.2.6 Releasing halt status by interrupt

Releasing the halt status by an interrupt is specified by the “HALT 1000B” instruction.

When releasing the halt status by an interrupt is specified, the halt status is released as soon as the interrupt has

been accepted.

Many interrupt sources are available as described in 12. INTERRUPTS. Which interrupt source is used to release

the halt status must be specified in advance in software.

To accept an interrupt, each interrupt request must be issued from each interrupt source and each interrupt must

be enabled (by setting the corresponding interrupt enable flag).

Therefore, the interrupt is not accepted even if the interrupt request is issued, and the halt status is not released.

When the halt status is released by accepting an interrupt, the program flow branches to the vector address of the

interrupt.

When the RETI instruction is executed after interrupt servicing, the program flow is restored to the instruction after

the HALT instruction.

If all the interrupts are disabled (DI status), the halt status is released by enabling an interrupt (IPxxx = 1) and issuing

an interrupt source (IRQxxx = 1), and the flow of the program goes to the instruction after the HALT instruction.

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