APS 6RL Series, Operation Manual

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6RL SERIES OPERATION MANUAL
SECTION 7: REMOTE PROGRAMMING
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2018 by Adaptive Power Systems, Inc. (APS) • All Rights Reserved • No reproduction without written authorization from APS.
6RL Series Regenerative DC Load Operation Manual Page 124 of 204
7.9 ModBus RTU Details
This protocol can be used with the USB-B interface (where available) and with most of the
optionally available interface modules. The addressed information when using ModBus
protocol is also called a register. This document uses the terms address, register or register
address.
Message Types
The message system distinguishes between query messages, control messages and response
messages. Query messages will cause the unit to send a response message, while control
messages only cause it to reply with a 1:1 echo, in order to confirm reception.
General
The units also support the text based SCPI language, with automatic detection of the used
protocol. When using ModBus, the first byte of every message has to be zero.
Functions
The second byte of a message contains a ModBus function code (FC, marked blue below),
which determines whether the message is a READ or WRITE message. It also determines,
whether one or multiple registers are accessed. The protocol, as described below, supports
following ModBus functions (Date: 07-13-2018):
Function Function name Description Example of use
Hex Dec Long Short
0x01 1 READ Coils RSC,
RC Always reads 1 bit, but is returned as a full
register with a 16-bit value. For example, the
value 0xFF00 means "logic 1" or TRUE. At
this point, it is different from the ModBus
standard and may cause problems with
ModBus software tools. Query the input /
output condition
0x03 3 READ Holding
Registers
RHR Used to read n subsequent registers. Results
in n*2 bytes of data in the response
message. Read the model
name string (1-40
bytes)
0x05 5 WRITE Single
Coil
WSC Used to write 16 subsequent bits which are
interpreted as 1 bit (TRUE or FALSE). At this
point, it is different from the ModBus
standard and may cause problems with
ModBus software tools. Switch unit to remote
control.
0x06 6 WRITE Single
Register
WSR Used to write one register. Set values (U, I, P
etc.)
0x10 16 WRITE Multiple
Registers
WMR Used to write n subsequent registers. Used
to write beyond the limits of a register block,
for example when trying to write multiple
set values (U, I, P) at once. Write multiple values
at once within a
register block or
write the so-called
user text.
Table 7-2: ModBus RTU Functions
Note: The register list defines which of the above functions may be used with every
register.