Jbus Protocol; Description; Principle; Synchronizing Data Exchanges - MGE UPS Systems SineWave JBUS Installation And User Manual

JBUS protocol

description

The JBUS protocol is designed to read
or write one or more bits and one or
more words.
For simplicity's sake we shall merely
describe the procedures required to
control and monitor the SineWave
active harmonic conditioner.
The exchanges take place at the
master's initiative and contain a master
question and a slave answer.
The master questions are sent to a
given slave (identified by its number in
the first byte of the question frame) as
shown in the diagram opposite:

principle

Detailed knowledge of the protocol is
necessary only if a computer is used for
the master which has to be
programmed accordingly:
Exchanges always contain two
messages: a master question and a
slave answer.
Each message or frame contains 4
types of information:
the slave number (1 byte) which
specifies the destination cubicle. If the
number is zero then the question
concerns all the slaves and there is no
answer message (this would then be a
broadcast message, a principle which
is not used in this application);
synchronizing data
exchanges
Any character received after 3 or more
character lengths of silence is
interpreted as the start of a frame.
MGE UPS SYSTEMS
TM
master
slave 1
slave N
physical
media
the function code (1 byte) which
selects a control (read, write, bit , word)
and checks that the answer is correct.
The JBUS protocol has 10 functions,
4 of which are used in our
application: function 3 (reading n
output or internal words), or function
4 (reading n input words), or
function 6 (writing 1 word), or
function 16 (writing n words).
We shall only look at these 4 functions
in the rest of the manual.
Therefore, a minimum silence of
6 character lengths between frames
must be respected.
SineWave™ JBUS communication system installation: E-51027160XT/AC
master
request
response
slave slave
response analysis
and preparation
of next ex change
wait
request
to slave 1
request
request processing
exchange i
contains the parameters for the
function: word address, word value,
number of words;
used to detect transmission errors.
slave
wait
request
to slave N
request
exchange i+1
the information field (N bytes) which
the control word (2 bytes) which is
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