ZiLOG Z8 User Manual page 66

Z8 Microcontrollers
I/O Ports
5.6 PORT HANDSHAKE (Continued)
RDY
(Input To Z8)
DAV
(Output From Z8)
Data on Port
(Output From Z8)
State 1.
RDY input is High indicating that the I/O device is ready to accept data.
The Z8 Writes to the port register to initiate a data transfer. Writing to the port outputs new data and
State 2.
forces
State 3.
The I/O device forces RDY Low after latching the data. RDY Low causes an interrupt request to be generated.
The Z8 can write new data responses to RDY going Low; however, the data is not output until State 5.
DAV
State 4. The
DAV
The
State 5.
5-20
1
DAV
Low if and only if RDY is High.
output from the Z8 is driven High in response to RDY going Low.
goes High, the I/O device is free to raise RDY High thus returning the interface to its initial state.
Figure 5-24. Z8 Output Handshake
2 3
Valid Data
ZiLOG
4 5
UM001601-0803