Document No.: FT_000138
VINCULUM-II EMBEDDED DUAL USB HOST CONTROLLER IC Datasheet
Version - 1.2
Clearance No.: FTDI# 143
6.3.3 Half Duplex, 4 pin
In half duplex mode, the MOSI signal is shared for both Master to Slave and Slave to Master
communications. When using 4 pins, the MISO signal carries the status bits. The Master initiates data
write transfer, this by asserting SS# and then sending out a command byte. This has the same format as
that shown in Figure 6-7. The Slave sends status during this command phase and if this indicates that
the Slave can accept data the Master will follow this up with a byte of write data. If the status continues
to indicate that more data can be written, a whole stream of data can be written following one single
command. The operation completes when the Master raises SS# again. Figure 6-8 is an example of this.
SS#
MOSI
MISO
8 bit CMD
STATUS
W0
W1
W2
STATUS
STATUS
STATUS
Figure 6-8 Half Duplex Data Master Write
Data reads are similar, apart from the MOSI pin changing from Slave input to Slave output after the
command phase. Figure 6-9 is an example. In this diagram, the Master drives the command while the
Slave returns with status. Then the MOSI buffers are turned round and a stream of read data is sent from
the Slave to the Master on the MOSI signal.
Master to Slave
Slave to Master
SS#
MOSI
MISO
8 bit CMD
STATUS
R0
R1
R2
STATUS
STATUS
STATUS
Figure 6-9 Half Duplex Data Master Read
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