Timing Diagram For Data Transfer Between The - Siemens SIMATIC S5 CP 523 Manual

CP 523
Data transfer between the CP and peripheral device takes place as follows:
The CP 523 sets the "DTR" output after startup. This indicates that the CP is operable and ready to
receive.
Example: The CP wants to send data
1. CP waits till DSR = ON
If the peripheral device still has not set DSR to ON after 20 s, the CP reports the error to the
CPU (peripheral device not ready).
2. CP sets RTS
3. CP waits till CTS = ON
If the peripheral device still has not set CTS to ON after 20 ms, the CP reports the error to the
CPU (peripheral device not ready).
4. CP sends data
5. CP resets RTS after sending data
6. Peripheral device sets CTS to OFF
1
TXD
0
ON
DTR
OFF
ON
RTS
OFF
1
RXD
0
ON
DSR
OFF
ON
CTS
OFF
CP switched
on
max:
20 s
Figure 2-5. Timing Diagram for Data Transfer between the CP and the Peripheral Device
Example: Peripheral device wants to send data
The peripheral device only checks the DTR line
If ON: Data may be sent (CP ready to receive)
If OFF: Data transmission must be interrupted (CP not ready to receive)
EWA 4NEB 811 6044-02a
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max:
.
20 s
.
Peripheral device switched on
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Technical Description
CP reports data
cannot be received
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