Zilog Z16C35 User Manual
Page 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
Page 170 of 316
UM011002-0808