Z8
®
CPU
User Manual
UM001604-0108
Input/Output Ports
63
Port Handshake
When Ports 0, 1, and 2 are configured for handshake operation, a pair of lines from Port 3
are used for handshake controls. The handshake controls are interlocked to properly time
asynchronous data transfers between Z8
®
and a peripheral. One control line (DAV) func-
tions as a strobe from the sender to indicate to the receiver that data is available. The sec-
ond control line (RDY) acknowledges receipt of the sender’s data, and indicates when the
receiver is ready to accept another data transfer.
In input mode, data is latched into the Port’s input register by the first DAV signal, and is
protected from being overwritten if additional pulses occur on the DAV line. This over-
write protection is maintained until the port data is read. In output mode, data written to
Port 0 Handshake Output
P35
RDY0/DAV0
Port 1 Handshake Output
P34
RDY1/DAV1
Port 2 Handshake Output
P36
RDY2/DAV2
Analog Comparator Input
P31
AN1
P32
AN2
P33
REF
Analog Comparator Output
P34
AN1-OUT
P35
AN2-OUT
P37
AN2-OUT
Interrupt Requests
P30
IRQ3
P31
IRQ2
P32
IRQ0
P33
IRQ1
Serial Input (UART)
P30
DI
Serial Output (UART)
P37
DO
SPI Slave Select
P35
SS
SPI Clock
P34
SK
Counter/Timer
P31
T
IN
P36
T
OUT
External Memory Status
P34
DM
Table 17. Port 3 Line Functions (Continued)
Function
Line
Signal