Zilog Z16C35 Manual do Utilizador descarregar pdf (Página 176)

Application Note

Interfacing Z80

CPUs to the Z8500 Peripheral Family

SOFTWARE CONSIDERATIONS - POLLED OPERATION

There are several options available for servicing interrupts

on the Z8500 peripherals. Since the vector of IP registers

can be read at any time, software can be used to emulate

the Z80 interrupt response. The interrupt vector read

reflects the interrupt status condition even if the device is

programmed to return to vector that does not reflect the

status change (SAV or VIS is not set). The code below is

a simple software routine that emulates the Z80 vector

response operation.

Z80 Vector Interrupt Response, Emulation by

Software

;This code emulates the Z80 vector interrupt

;operation by reading the device interrupt

;vector and forming an address from a vector

;table. It then executes an indirect jump to

;the interrupt service routine.

INDX: LD A,CIVREG ;CURRENT INT. VECT. REG

OUT (CTRL), A ;WRITE REG. PTR.

IN A, (CTRL) ;READ VECT. REG.

INC A ;VALID VECTOR?

RET Z ;NO INT - RETURN

AND 00001110B ;MASK OTHER BITS

LD E,A

LD D,0 ;FORM INDEX VALUE

LD HL,VECTAB

ADD HL,DE ;ADD VECT. TABLE ADDR.

LD A, (HL) ;GET LOW BYTE

INC HL

LD H, (HL) ;GET HIGH BYTE

LD L,A ;FORM ROUTINE ADDR.

JP (HL) ;JUMP TO IT

VECTAB:

DEFW INT1

DEFW INT2

DEFW INT3

DEFW INT4

DEFW INT5

DEFW INT6

DEFW INT7

DEFW INT8

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