User`s manual

Serial Control Port Configuration
CS485xx Hardware User’s Manual
DS734UM7 Copyright 2009 Cirrus Logic, Inc. 3-6
Figure 3-5. Data Byte with ACK and NACK
After an ACK or NACK from the master or slave, the slave must leave the SCP_SDA line high so the master
can then generate either a Stop condition to abort the transfer, or a another Start condition to start a new
transfer.
Figure 3-6. Stop Condition with ACK and NACK
If a slave can’t receive or transmit another complete byte of data until it has performed some other function,
for example servicing an internal interrupt, it can hold the SCP_CLK line low to force the master into a wait
state. Data transfer then continues when the slave is ready for another byte of data and releases SCP_CLK.
Start
S
CP_CLK
S
CP_SDA A[6] A[5] A[4] A[3] A[2] A[1] A[0] R/W
ACK
Data Byte
ACK
M S M SWrite
M S S MRead
Start
S
CP_CLK
S
CP_SDA A[6] A[5] A[4] A[3] A[2] A[1] A[0] R/W
ACK
Data Byte
NACK
M S M SWrite
M S S MRead
M = Master Drives SDA
S = Slave Drives SDA
Stop
S
CP_CLK
S
CP_SDA Data Byte
ACK
M S MWrite
Read
S M M
Stop
S
CP_CLK
S
CP_SDA Data Byte
NACK
M S M
Write
Read
S M M
M = Master Drives SDA
S = Slave Drives SDA