Kramer Electronics VS-4228 - Manual (Page 10)

VS-4228 - Overview 7
A master device always transmits over pins 3 and 8 and receives over 2 and 7.
A slave device always transmits over pins 2 and 7 and receives over 3 and 8.
The communication path must be kept clear between the master and slave units in
both directions, since the slave device must respond to any command transmitted
by the master. If the master receives no response from the slave, the master
cancels the communication with the slave machine and sometimes flags a
message: no communication.
For example, in video production when a special controller (with play and rewind
functionality) is the master device, each command transmitted to the slave device
must reach that slave device and that slave device must respond, otherwise the
master device disconnects.
3.2.3 Device Definition
In many broadcast applications, different machines involved in production can be
either slaves or masters. Using a device as a master means that the device talks
via pins 3 and 8 and listens via pins 2 and 7. In another setup, that uses the same
device as a slave, this means that the device talks via pins 2 and 7 and listens via
pins 3 and 8.
For example, an edit controller always works as a master. During an editing
session, a VTR may be the slave to the edit controller. However, in a duplication
setup, the VTR may become a master for a second VTR.
3.2.4 Automatic Configuration
After connecting the 9-pin D-sub connectors and cables between the controlled
units, the VS-4228 automatically configures which pins to use in the 9-pin D-sub
connector according to the assignment of each machine.
3.2.5 Port Definitions
Modern equipment usually has only one connector, RS-422, which functions as a
master as well as a slave.