Reference
MVI56E-MNETR ♦ ControlLogix Platform
User Manual
Modbus TCP/IP Interface Module with Reduced Data Block
Page 134 of 175
ProSoft Technology, Inc.
June 14, 2011
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.
5.5.3 Read Input Status (Function Code 02)
Query
This function allows the user to obtain the ON/OFF status of discrete inputs in the
addressed Server PC Broadcast mode is not supported with this function code.
In addition to the Server 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 will be interrogated to obtain status data.
The addressing allows up to 2000 inputs to be obtained at each request;
however, the specific Server 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 Server number 11.
Adr
Func
Data Start Pt Hi
Data Start Pt Lo
Data #of Pts Hi
Data #of Pts Lo Error Check Field
11
02
00
C4
00
16
CRC
Response
An example response to Read Input Status is as shown in Figure C4. The data is
packed one bit for each input. The response includes the Server address,
function code, quantity of data characters, the data characters, and error
checking. Data will be packed with one bit for each input (1=ON, 0=OFF). The
lower order bit of the first character contains the addressed input, and the
remainder follow. For input quantities that are not even multiples of eight, the last
characters will be filled in with zeros at high order end. The quantity of data
characters is always specified as a quantity of RTU characters, that is, the
number is the same whether RTU or ASCII is used.
Because the Server interface device is serviced at the end of a controller's scan,
data will reflect input status at the end of the scan. Some Servers will limit the
quantity of inputs provided each scan; thus, for large coil quantities, multiple PC
transactions must be made using coil status for sequential scans.
Adr
Func
Byte
Count
Data Discrete Input
10197 to 10204
Data Discrete Input
10205 to 10212
Data Discrete Input
10213 to 10218
Error Check Field
11
02
03
AC
DB
35
CRC
