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
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