Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 442)

Section 8
Communication Interface
8-9
RS-491 Level I and Level II protocol are used for data communication
between the control and peripherals. They provide a structured process of
communication through the RS-232 or RS-422 interface ports.
Level I protocol is used for data communication between the control and a
simple peripheral, a printer for example. When communication between
the control and a simple peripheral has been established, the following
three signals are used to control data transmission start/stop:
RS (request to send)
CS (clear to send)
DM (data set ready) Port B only
Data Receiving Sequence
When the control receives data from a peripheral, CS and RS signals are
used to control the communication, see Figure 8.10. The peripheral
confirms that the control is ready for data reception by the CS (clear to
send) signal before it transmits the data.
Figure 8.10
Data Reception Sequence
Signal flow
Peripheral
RS
CS
SD
1 2 3 4 5 6 7 9 8
CNC
11354-I
The control receives data from the peripheral in the following sequence.
The numbers correspond to those in Figure 8.10.
8.7
Protocol
8.7.1
RS-491 Level 1 Protocol