Function 23 (17Hex): "Read/Write Multiple Registers; Exception Codes - Pepperl+Fuchs VBG-ENXK20-DMD-EV Manual

AS-i 3.0 EtherNet/IP+Modbus TCP Gateway
Operation via Ethernet IP (Modbus/TCP)
12.2.3

Function 23 (17hex): "Read/Write multiple registers"

This function allows to read the value of read/write-registers and the setting of
several read/write-registers:
request: 17
response:
D1 ... Dn: register value
Example:
Read 2 registers at reference 0 and write 1 register at reference 3 of value 4660
returning values 4 and 4951.
.
request:
request:
response:
response:
12.2.4

Exception codes

There is a defined set of exception codes to be returned by slaves in the event of
problems. Note that masters may send out commands "speculatively", and use
the success or exception codes received to determine which MODBUS com-
mands the device is willing to respond to and to determine the size of the various
data regions available on the slave.
All exceptions are signaled by adding 128 to the function code of the request, and
following this byte by a single reason byte for example as follows:
For instance:
RR RR NR
high low high
NW NW B
high low
17 B D1 D1
high low
RR: reference number for read (2 byte hex-value of register)
NR: word count for read (1 - 125) (2 byte)
RW: reference number for write (2 byte hex-value of register)
NW: word count for write (1 - 100) (2 Byte)
B: byte count (B = 2 x word count for write / 1 byte)
(redundant information to Word count but necessary)
17 RR RR NR
high low high
17 00 00 00
17 B D1 D1
high low
17 04 00 04
NR RW RW
low high low
D1 D1 ...
high low
... Dn Dn
high low
NR RW RW NW
low high low high
02 00 03 00
D2 D2
high low
49 51
Dn
low
NW B D1 D1
low high low
01 02 46 60
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