ProSoft Technology MVI69L-MBS - Manual (Page 110)

Reference MVI69L-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 110 of 154 ProSoft Technology, Inc.
January 6, 2014
Node
Address Function
Code Data Start
Point High Data Start
Point Low Number of
Points High Number of
Points Low Error Check Field
(2 bytes)
0B 03 00 6B 00 03 CRC
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.
Because the Slave interface device is normally serviced at the end of the
controller's scan, the data reflects the register content at the end of the scan.
Some Slaves limit the quantity of register content provided each scan; thus for
large register quantities, multiple transmissions are made using register content
from sequential scans.
In the example below, the registers 40108 to 40110 have the decimal contents
555, 0, and 100 respectively.
Node
Address Function
Code Byte
Count Hi
Data Lo
Data Hi
Data Lo
Data Hi
Data Lo
Data Error Check Field
(2 bytes)
0B 03 06 02 2B 00 00 00 64 CRC
7.2.5 Read Input Registers (Function Code 04)
Query
This Function Code obtains the contents of the controller's input registers from
the Modbus 3x range. These locations receive their values from devices
connected to the I/O structure and can only be referenced, not altered from within
the controller, The addressing allows up to 125 registers to be obtained at each
request; however, the specific Slave device may have restrictions that lower this
maximum quantity. The registers are numbered for zero (30001 = zero, 30002 =
one, and so on). Broadcast mode is not allowed.
The example below requests the contents of register 30009 in Slave number 11.
Node
Address Function
Code Data Start
Point High Data Start
Point Low Number of
Points High Number of
Points Low Error Check
Field (2 bytes)
0B 04 00 08 00 01 CRC