Datasheet
Vinculum-II Embedded Dual USB Host Controller IC
Version 1.7
Document No.: FT_000138 Clearance No.: FTDI#143
6.3.4 Half Duplex, 3 pin
The 3 pin half duplex mode eliminates the MISO pin from the protocol. This means that status bytes need
to be sent on the MOSI pin. Again the Master initiates a transfer by asserting SS# and sending out a
command byte. The Slave sends status back to the Master. If a write has been requested and the status
indicates that the Slave can accept data, MOSI should be changed to an output again and data will be
sent fromMaster to Slave.
Following this data, the Slave will send a further status byte if SS# remains active. If the status indicates
that more data can be written, the next data byte can be sent to the Slave and this process continues
until SS# is de-asserted. Figure 6.10 is an example of this:
Master to Slave Slave to Master Master to Slave Slave to Master
Master to Slave
SS#
MOSI
8 bit CMD
STATUS
W0
STATUS
W1
Figure 6.10 Half Duplex 3-pin Data Master Write
Data reads are similar expect that after the command byte all data transfer is from Slave to Master.
Figure 6.11 is an example of this:
Master to Slave
Slave to Master
SS#
MOSI
8 bit CMD
STATUS
R0
STATUS
R1
Figure 6.11 Half Duplex 3-pin Data Master Read
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