260 • I/O modules
Data exchange modules 750-654
Modular I/O System
ETHERNET TCP/IP
The control byte consists of the following bits:
Bit 7
Bit
6
Bit
5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
X
X
X
X
X
X
X
Constant value
always should
be 0.
Not used
The status byte consists of the following bits:
Bit7
Bit
6
Bit
5
Bit4
Bit3
Bit2
Bit1
Bit0
0
X
X
RCVT1
RCVT2
CHK
OVR
PAR
Constant
value always
should be 0.
Module is in
timeout.
All output bits
are set to 0
(watchdog).
The recei-
ver is in
timeout.
Checksum
error.
Buffer
overflow
Parity
error or
wrong
data in a
frame.
The PLC is able to control transmission and reception of data by means of the
control byte and the status byte.
Control of the multiplex connection:
In the process image of the transmitting buscoupler, one Bit is set to "1" for the
whole time. As long as this Bit is "1" in the receiving coupler, further input
Bits can be evaluated. If the Bit is "0" the multiplex connection has been dis-
rupted. The further Bits are also 0 because of the watchdog.
Control of the multiplex connection with acknowledge:
If the transmitting buscoupler gets an acknowledge from the receiving buscou-
pler, the received bit must be transfered as an output bit to the process image.
The transmission is successful as long as the Bit is "1".
Handshake:
If a serial data exchange should be made with the data exchange module, the
handshake can be made via "Toggle Bits". Therefore an input bit and an output
bit are reserved. As soon as those bits are different from each other, a request
from the opposite module is made. As soon as the request is executed the out-
put bit is toggled