BECKHOFF FM33xx - Manual (Page 31)

I/O configuration
26 FM33xx
Protocol for the cyclical data transfer in
multiplex mode
The following protocol has been specified for communication with the TC-
Plug module in order to reduce the quantity of data transferred over the
fieldbus.
Appropriate channel selection request bits are set by the PLC in the control
byte. The channel selection request bits select the 4 channels that are to
be transferred. The TC-Plug copies the corresponding data in the input
bytes [1-8] and confirms it in the channel confirmation bits of the status
byte. If the control byte == status byte, then the data is valid.
Control byte Value Description
Channel Selection Request
Bits 0-3 0 no channel selected
1 Channel 0-3 in Input Data [1..8]
2 Channel 4-7 in Input Data [1..8]
3 Channel 8-11 in Input Data [1..8]
4 Channel 12-15 in Input Data [1..8]
5 Channel 16-19 in Input Data [1..8]
6 Channel 20-23 in Input Data [1..8]
7 Channel 24-27 in Input Data [1..8]
8 Channel 28-31 in Input Data [1..8]
9 Status (Open circuit Channel 0-31 in Input Data [1..4] and Back Voltage in
Input Data [5..8])
Bit 4-6 - Reserved for future use
Bit 7 1/0 Toggle-Bit Measure Control
Status byte Value Description
Channel Selection
Confirmation Bits 0-3 0 no channel selected
1 Channel 0-3 in Input Data [1..8]
2 Channel 4-7 in Input Data [1..8]
3 Channel 8-11 in Input Data [1..8]
4 Channel 12-15 in Input Data [1..8]
5 Channel 16-19 in Input Data [1..8]
6 Channel 20-23 in Input Data [1..8]
7 Channel 24-27 in Input Data [1..8]
8 Channel 28-31 in Input Data [1..8]
9 Status (Open circuit Channel 0-31 in Input Data [1..4] and Back Voltage in
Input Data [5..8])
Bit 4-6 - Reserved for future use
Bit 7 1/0 Toggle-Bit Measure Status
The AD conversion of the thermocouple input data in the TC-Plug module
can be initiated by the PLC by toggling bit 7 in the control byte. After the bit
has been toggled, the status and control bytes have different values in
bit 7. When the measuring cycle in the TC-Plug module has been
completed the TC-Plug will also toggle bit 7 in the status byte. The toggled
bits in the status and control bytes then have the same value.
By setting the appropriate channel selection request bits the PLC can then
request the current thermocouple input data. Every request in the control
byte is appropriately acknowledged in the status byte by the TC-Plug.
During a conversion procedure the TC-Plug converts all its active
configured channels. Once completed, the PLC can request the channel
data over a number of cycles.