Filter
Top Products
6739389EN/FB - Page 7
JBUS protocol (continued)
Principle
A full understanding of the protocol
is only required if the master is a
computer that must be
programmed.
All communications include 2
messages: a request from the
master and a response from the
slave.
Each message or frame containes
4 types of information:
◗ slave address (1 byte)
The slave address specifies the
destination station (see address
list):
◗ ◗ unitary rectifier-inverter cubicle,
◗ ◗ parallel rectifier-inverter cubicle,
◗ ◗ Static Switch cubicle.
If zero, the request addresses all
slaves and there is no response
message (in which case it is a
broadcast message, a function 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.
Therefore, a minimum silence of 3
character lengths between frames
must be respected.
◗ function code (1 byte)
Selects a command (e.g. read or
write a bit or a word) and checks
that the response is correct.
The JBUS protocol comprises 10
functions of which 3 may be used in
this application: function 3 (read n
output or internal words), or
function 4 (read n input words), or
function 16 (write n words);
◗ information field (n bytes)
The information field contains the
parameters related to the functions:
bit address, word address, bit
value, word value, number of bits,
number of words;
◗ check word (2 bytes)
A word used to detect transmission
errors.
Description of request and response frames
information
check word
request
1 byte
1 byte
n bytes
2 bytes
When the message is
received, the slave reads
the check word and accepts
or refuses the message
This function code selects one of
10 possible commands:
- Function 1 : read n output or internal bits
- Function 2 : read n input bits
- Function 3 : read n output or internal words
- Function 4 : read n input words
- Function 5 : write one bit
- Function 6 : write one word
- Function 8 : data exchange diagnostics
- Function 11 : read event counter
- Function 15 : write n bits
- Function 16 : write n words
information requested: bit/word address,
bit/word value, bit/word number.
slave adress
(1 à FF)
function
code
data
response
values of bits or words read
values of bits or words written
number of bits or words
slave adress
(1 à FF)
function
code
CRC
check word
2 bytes
◗ bytes
1 byte1 byte