UPD17708 datasheet(95/356 Pages) NEC

95 / 356 page

µPD17704, 17705, 17707, 17708, 17709

10.5 Using Data Buffer Stack

A program example is shown below.

Example To save the contents of the data buffer and address register by using INT0 interrupt routine (the

contents of the data buffer and address register are not automatically saved when an interrupt

occurs).

START:

INITIAL

; Reset address

; Interrupt vector address

NOP

; SI01

NOP

; SI00

NOP

; TM3

NOP

; TM2

NOP

; TM1

NOP

; TM0

NOP

; INT4

NOP

; INT3

NOP

; INT2

NOP

; INT1

INTINT0

; INT0

NOP

; Down edge of CE

INTINT0:

PUT

DBFSTK, DBF ; Saves contents of DBF to first level of data buffer

; stack (DBFSTK)

GET

DBF, AR

; Transfers contents of address register (AR) to DBF

PUT

DBFSTK, DBF ; Saves contents of AR to second level of data buffer

; stack

Processing B

; INT0 interrupt processing

GET

DBF, DBFSTK ; Restores second level of data buffer stack to data buffer,

PUT

AR, DBF

; and restores contents of data buffer to address register

GET

DBF, DBFSTK ; Restores first level of data buffer stack to data buffer

RETI

INITIAL:

SET1 IP0

LOOP:

Processing A

LOOP

END

10.6 Cautions on Using Data Buffer Stack

The contents of the data buffer stack are not automatically saved when an interrupt is accepted, and therefore,

must be saved by software.

Even when a bank of the data memory other than BANK0 is specified, the contents of the data buffer (existing

in BANK0) can be saved or restored by using the “PUT” and “GET” instructions.

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