KROHNE MFC 010 C Converter - Manual (Page 25)

MFC010 Interface Manual 23
6. Modbus Functions Supported by the MFC010
6.1 01 (01
16
): Read Coil Status
This function permits the user to read the state of a number of consecutive Discrete Outputs, or “Coil”,
registers. Within the MFC010 the majority of the Discrete Outputs are used to initiate command functions;
when read, response will be “ 1” w hilst c ommand i s bei ng processed and “ 0 when t he c ommand i s
completed (See Section 7.2 on page 39 for details of the individual Status Output registers). The format
of the Master request telegram for this function should be as follows.
Request
Character
Field For Example
1 Slave Address 01
16
Request to Slave ID 1
2 Function 01
16
“Read Coil Status”
3 Start Address Hi 03
16
Start Address = 1002
4 Start Address Lo E9
16
5 No of Points Hi 00
16
No. of Points = 5
( “Coils” 1002 – 1006 ) 6 No of Point Lo 05
16
7 CRC Lo 2D
16
CRC Checksum
8 CRC Hi B9
16
The MFC010 will respond to such a request with a telegram formatted as follows.
Response
Character
Field For Example
1 Slave Address 01
16
Response from Slave ID 1
2 Function 01
16
“Read Coil Status”
3 Data Bytes in Response 01
16
1 byte (5 States requested < 8 Bits)
4 Data Byte 1 15
16
Data = 00010101
2
5 CRC Lo 90
16
CRC Checksum
6 CRC Hi 47
16
The number of data bytes in the response will depend upon the number of Discrete Outputs requested.
The appropriate bit in each of the data bytes received will indicate each Discrete Output state requested.
Therefore, each data byte in the response will contain a maximum of 8 Discrete Output “Coil” states. For
example, if 19 Discrete Outputs are requested, then three data characters will be r eturned, with the first
group of 8 output states encoded in the first data byte, the second group of 8 output states coded in the
second data byte, and the last 3 output states coded in the first three bit locations of the last data byte.
Bit 0 of the first response data byte will c orrespond t o t he “ Start A ddress” D iscrete O utput r egister
specified by the request telegram. B it 0 of the second response data byte will correspond to the “Start
Address” + 8 Discrete Output register and so on.
In the example above, 5 Discrete Outputs are r equested, s o onl y one dat a by te i s r equired i n t he
response. The response data value shown above i ndicates t hat r egisters 1002, 1004 and 1006 ar e
active, and that registers 1003 and 1005 are inactive.