IOBUS1 datasheet(45/88 Pages) FTDI

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Datasheet

Vinculum-II Embedded Dual USB Host Controller IC

V ers ion 1 .7

Doc ument N o.: FT _000138 C learance N o.: FT DI# 1 43

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#

MISO

MOSI

8 bit CMD

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.

SS#

MISO

MOSI

8 bit CMD

STATUS

Master to Slave

Slave to Master

Figure 6.9 Half Duplex Data Master Read

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