ZiLOG Z80 Handbook page 102

pothesizing a paper-tape-reader controller with interrupt capability.
Fig. 7-3 shows the interrupt action. When the next frame of tape
has been read, the paper-tape controller brings the INT line low.
When the interrupt is recognized by the CPU, lines IOR and VIII
are brought low (not to scale in figure). This is decoded by the
controller as an interrupt acknowledge and the controller jams an
RST 20H instruction onto the data bus. The CPU executes the RST
20H, pushing the contents of the program counter (3332H) into the
stack and transferring control to page 0 location 20H. At 2014 a JP
FEEOH is executed to transfer control to the paper-tape interrupt
(1) NEXT
FRAME
I
PAPER TAPE
READER
CONTROLLER
(6)
RETURN TO
3332H
SP
SP
l (3)
SAVE LOCATION
J
OF INTERRUPT
(4) INTERRUPT PROCESSING AT 20H
MEMORY
LOCATION INSTRUCTION
0020H JMP FEEOH
(A PAPER TAPE INTERRUPT
PROCESSING ROUTINE
FEEOH PUSH AF
FEE1H PUSH BC
FEE2H
PUSH DE
FEE3H PUSH HL
OTHER PROCESSING
FEFOH
POP HL
FEF1H POP DE
FEF2H
POP BC
FEF3H
POP AF
FEF4 I E l
FEF5H RET I
Fig. 7 -3. Mode 0 interrupt processing.
INT
RESTART
20H
(2) CONTROLLERICPU
INTERRUPT
COMMUNICATION
109