IOBUS0 datasheet(46/88 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

6.3.4 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 from Master 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:

SS#

MOSI

8 bit CMD

Master to Slave

STATUS

Slave to Master

Master to Slave

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:

SS#

MOSI

8 bit CMD

Master to Slave

STATUS

Slave to Master

Figure 6.11 Half Duplex 3-pin Data Master Read

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