MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 171 of 209
Data Discrete Input
10197 to 10204
Data Discrete Input
10205 to 10212
Data Discrete Input
10213 to 10218
The status of inputs 10197 to 10204 is shown as AC (HEX) = 10101 1100
(binary). Reading left to right, this show that inputs 10204, 10202, and 10199 are
all on. The other input data bytes are decoded similar.
Due to the quantity of input statuses requested, the last data field which is shown
as 35 HEX = 0011 0101 (binary) contains the status of only 6 inputs (10213 to
102180) instead of 8 inputs. The two left-most bits are provided as zeros to fill
the 8-bit format.
6.8.4 Read Holding Registers (Function Code 03)
Query
Read Holding Registers (03) allows the user to obtain the binary contents of
holding registers 4xxxx in the addressed Slave. The registers can store the
numerical values of associated timers and counters which can be driven to
external devices. The addressing allows up to 125 registers to obtained at each
request; however, the specific Slave device may have restriction that lower this
maximum quantity. The registers are numbered form zero (40001 = zero, 40002
= one, and so on). The broadcast mode is not allowed.
The example below reads registers 40108 through 40110 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.
Response
The addressed Slave responds with its address and the function code, followed
by the information field. The information field contains 1 byte describing the
quantity of data bytes to be returned. The contents of the registers requested
(DATA) are two bytes each, with the binary content right justified within each pair
of characters. The first byte includes the high order bits and the second, the low
order bits.
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