Sensoray 2426 - Manual (Page 15)

2426 Instruction Manual 13 Serial Communication Interface
9.4.1 RS-422 with a Single Master
In this case, the 2426 module is the sole master of the device
network and one or more remote slaves reside on the network.
No other devices are permitted to transmit on the master’s
transmit pair. Figure 16 shows a network of this type with two
slave devices.
Figure 16: Single-master RS-422 device network
Multiple slave devices must never simultaneously drive the
master’s receive pair. This is typically ensured by assigning
unique addresses to the slaves and programming them so that
they will drive the master’s receive pair only when responding
to directed command messages from the master.
9.4.2 RS-422 with Multiple Masters
In a multi-mastered device network, the 2426 comport shares
its transmit pair with one or more remote masters. Figure 17
shows an example of this in which the device network has two
masters and one slave.
Figure 17: Multi-mastered RS-422 device network
Care must be taken to ensure that masters do not drive their
shared transmit pair at the same time, as transmitter collision
detection is not available in this configuration.
9.4.3 RS-485
RS-485 networks employ a single pair for both transmit and
receive. Only one transmitter is permitted to drive the
common pair at a time. Figure 18 shows an RS-485 network
with one master (the 2426) and two slaves, although it is
possible to utilize more than one master on a device network.
Figure 18: Single-master RS-485 device network
Remote 2426
Slave
Remote
Slave
Master
Remote
Slave
Remote
Master
2426
Master
Remote 2426
Slave Master
Remote
Slave