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FOM LINE DRIVER—ST AND S M
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3.2 Master/Slave Mode
When the master sends data to the transmitter (TX) of the RS-232 DB9, the 20-mA current loop, or the
RS-485 terminal block, the data is passed through to the master’s B optical port. From there, it is
daisychained to each slave’s B optical RX. As each slave receives the data, it is passed through to the DB9
RX and the receive (RX) terminal block. When the data reaches the slave that needs to respond, it will
send data to the optical A TX port and out to the next daisychained slave in the direction of the master.
The information is retransmitted and travels from daisychained slave to slave in the direction of the
master until it reaches the master’s Port A. Figure 3-2 illustrates this configuration.
Although the information is traveling through the other slaves, slaves don’t “see” data from other slaves.
This keeps the slaves from having to stop working in order to translate another slave’s information.
Figure 3-2. One unit configured as a master, all others as slaves.
As you look at the example above, keep these things in mind.
• Data flow is half-duplex only.
• The master transmits out of Port B only.
• Slaves transmit out of Port A only, and that transmission goes to the master.
• When a slave receives data in Port A, the data is looped back out Port A.
• When a slave receives data in Port B, the data is looped back out Port B and is sent out the DB9 port
(from the master).
• The master receives in Port A only.
TX RX TX RX TX RX TX RX TX RX TX RX TX RX TX RX
A B A B A B A B
TX RX TX RX TX RX TX RX TX RX TX RX TX RX TX RX
B A B A B B A A
Fiber
Cabling
Master
Transmitting
Receiving
Master Slave Slave Slave
Slave
Receiving
Receiving
Slave
Receiving
Transmitting
Slave
Receiving
Receiving
Data
Path