Datasheet
Vinculum-II Embedded Dual USB Host Controller IC
Version 1.7
Document No.: FT_000138 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 whenthe 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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