KROHNE MFC 010 C Converter - Manual (Page 26)

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MFC010 Interface Manual
6.2 02 (02
16
): Read Discrete Input
This function permits the user to read the state of a number of consecutive Discrete Input registers. (See
Section 7.3, on page 41, for details of the individual 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 02
16
“Read Discrete Input”
3 Start Address Hi 03
16
Start Address = 1001
4 Start Address Lo E8
16
5 No of Points Hi 00
16
No. of Points = 12
( “Inputs” 1001 – 1011 ) 6 No of Point Lo 0C
16
7 CRC Lo F8
16
CRC Checksum
8 CRC Hi 7F
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 02
16
“Read Discrete Input”
3 Data Bytes in Response 02
16
2 bytes
4 Data Byte 1 CD
16
Data = 11001101
2
5 Data Byte 2 09
16
Data = 00001001
2
6 CRC Lo 2D
16
CRC Checksum
7 CRC Hi 2E
16
The num ber of dat a by tes i n t he r esponse will depend upon the number of Discrete Inputs requested.
The appropriate bit in each of the data bytes received will indicate each Discrete Input state requested.
Therefore, each data by te i n t he r esponse w ill c ontain a m aximum of 8 di screte i nput s tates. F or
example, if 19 Discrete Inputs are requested, then three data characters will be returned, with the first
group of 8 input states encoded in the first data byte, the second group of 8 i nput states coded in the
second data byte, and the last 3 input states coded in the first three bit locations of the last data byte. Bit
0 of the first response data byte will correspond to the “Start Address” Discrete Input register specified by
the request telegram. B it 0 of the second response data byte will correspond to the “Start Address” + 8
Discrete Input register and so on.
In the example above, 12 Discrete Inputs are requested, so two data bytes are required in the response.