ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 162)

Reference MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 162 of 199 ProSoft Technology, Inc.
June 18, 2014
Because the Slave interface device is serviced at the end of a controller's scan,
data reflects coil status at the end of the scan. Some Slaves limit the quantity of
coils provided each scan; thus, for large coil quantities, multiple PC transactions
must be made using coil status from sequential scans.
Adr Func Byte
Count Data Coil
Status 20 to
27
Data Coil
Status 28 to
35
Data Coil
Status 36 to
43
Data Coil
Status 44 to
51
Data Coil
Status 52 to
56
Error
Check
Field
0B 01 05 CD 6B B2 OE 1B CRC
The status of coils 20 to 27 is shown as CD(HEX) = 1100 1101 (Binary). Reading
left to right, this shows that coils 27, 26, 23, 22, and 20 are all on. The other coil
data bytes are decoded similarly. Due to the quantity of coil statuses requested,
the last data field, which is shown 1B (HEX) = 0001 1011 (Binary), contains the
status of only 5 coils (52 to 56) instead of 8 coils. The 3 left most bits are
provided as zeros to fill the 8-bit format.
6.8.3 Read Input Status (Function Code 02)
Query
This function allows the user to obtain the ON/OFF status of discrete inputs in the
addressed Slave PC Broadcast mode is not supported with this function code. In
addition to the Slave address and function fields, the message requires that the
information field contain the initial input address to be read (Starting Address)
and the number of locations that are interrogated to obtain status data.
The addressing allows up to 2000 inputs to be obtained at each request;
however, the specific Slave device may have restrictions that lower the maximum
quantity. The inputs are numbered form zero; (input 10001 = zero, input 10002 =
one, input 10003 = two, and so on, for a 584).
The following table is a sample read input status request to read inputs 10197 to
10218 from Slave number 11.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display.
Adr Func Data Start Pt Hi Data Start Pt Lo Data #of Pts Hi Data #of Pts Lo Error Check Field
0B 02 00 C4 00 16 CRC