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RS 485 Communication Description
Communication RS 485 serial port connections
Transmission Channel Characteristics
levels:
RS 485
baud rate:
9600/4800/2400/1200/600
programmable
character length:
8 bits
parity:
none
stop bit:
1 bit
protocoll:
master (PC) / slave (converter)
max. devices:
32
Message Structure
(request and answer have the same format)
The master system (PC) starts every session sending
the following message to the slave units connected:
<STX> / <ADDR> + <WINDOW> + <COMMAND> +
<DATA> + <ETX> + <CRC>
where:
<STX> =
0x02
<ADDR> =
0x80 + device number (0...31)
0xFF: brodcasting command
(recognized by all the devices, it
doesn't implicate any answer)
(for RS 485 only)
<WINDOWS>=
' 000 '...' 999' window number
the meaning of the window
depends to the device type
<COMMAND>=
0x30: window value reading
0x31: window writing
<DATA> =
alphanumeric ASCII string
containing, in the case of writing
operation,the parameter to input
into the window addressed by
the field <WINDOW>This field
may have variable length
according to the data type
contained in the window where
you are working in. In the case of
Reading request of a window, the
data field doesn't exist.
<ETX>=
0x03
<CRC>=
XOR among all the characters
following <STX>= (with exception of
<STX>), including the end character
<ETX> hexadecimally encoded by
two ASCII characters.
When a slave device is addressed by the master:
In case of reading request of the value contained in
a window, the slave answers a string equal to the
one sent by the master but in addition there is the
field
<DATA>
window.The format of the field <DATA> depends to
the window type.
The different types are:
Logic (L)
Numeric (N)
Alphanumeric (A)
59
TECHNICAL INFORMATION
containing
the
value
Length
Characters
Permitted
1
'0'=OFF
'1'=ON
6
'0'...'9'
(Justifield to the right
with '0')
max 10
' '...'_'
87-900-873-01 (C)
of
the
Publicidad
