254 • I/O modules
RS485C interface 750-653
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
OL 2
OL1
OL0
0
IR
RA
TR
Constant
value
should
lways be 0.
Frames available in output area
OL2 is always 0,
i.e. OL2, OL1, OL0 = 0,1,1
3 characters should be sent and put
into the output.
Constant
value
should
always be
0.
Initialization
request
Receive
acknow-
ledge
Transmit
request
The status byte consists of the following bits:
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
IL2
IL1
Il0
BUF_F
IA
RR
TA
Constant
value
should
always be
0.
Frames available in input area IL2 is
always 0.
i.e. IL2, IL1, IL0 = 0,1,0
2 characters were received and
reside in input 0 and input 1.
Inpput
buffer is
full.
Initialization
acknow-
ledge
Receive
request
Transmit
acknow-
ledge
The PLC is able to control transmission and reception of data by means of the
control byte and the status byte.
Initialization of the module:
•
set IR bit in the control byte to "1"
•
transmit/receive functions are blocked
•
output/input buffers are erased
•
serial interface module will load its configuration data
Transmitting data:
•
TR
≠
TA: put characters into output bytes 0 to 2
•
amount of characters is specified in OL0 to OL2
•
TR is inverted and read out
•
characters are put into output buffer if TR=TA
Receiving data:
•
RR
≠
RA: input bytes 0 to 2 characters are available
•
amount of characters is specified in IL0 to IL2
•
characters in IL0 to IL2 are read out
•
RA is inverted and read out
•
all characters are read when RR=RA
The transmitting and receiving of data can be done simultaneously. The initia-
lization request has prioirity and will stop transmitting and receiving of data
immediately.
Attention
Resetting the initialization bit can be performed with the following message.
Message: input buffer full (Bit 3)
Input buffer is full. Data which is being currently received is now lost.
Содержание I/O-SYSTEM 750
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