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RS 232/RS 485 COMMUNICATION
DESCRIPTION
Both the RS 232 and the RS 485 interfaces are
available on the connector P2.
The communication protocol is the same (see the
structure below), but only the RS 485 manages the
address field. Therefore to enable the RS 485 is
necessary to select the type of communication as
well as the device address by means of the Navi-
gator software.
Communication Format
• 8 data bit
• no parity
• 1 stop bit
• baud rate: 600/1200/2400/4800/9600 pro-
grammable
Communication Protocol
The communication protocol is a MASTER/SLAVE
type where:
• Host = MASTER
• Controller = SLAVE
The communication is performed in the following
way:
1. the host (MASTER) send a MESSAGE + CRC to
the controller (SLAVE);
2. the controller answer with an ANSWER + CRC
to the host.
The MESSAGE is a string with the following format:
<STX>+<ADDR>+<WIN>+<COM>+<DATA>+<ETX>
+<CRC>
where:
NOTE
When a data is indicated between two quotes ('...')
it means that the indicated data is the correspond-
ing ASCII character.
− <STX> (Start of transmission) = 0x02
− <ADDR> (Unit address) = 0x80 (for RS 232)
<ADDR> (Unit address) = 0x80 + device num-
ber (0 to 31) (for RS 485)
− <WIN> (Window) = a string of 3 numeric char-
acter indicating the window number (from '000'
to '999'); for the meaning of each window see
the relevant paragraph.
− <COM> (Command) = 0x30 to read the window,
0x31 to write into the window
− <DATA> = an alphanumeric ASCII string with
the data to be written into the window. In case
of a reading command this field is not present.
The field length is variable according to the
data type as per the following table:
DATA TYPE
Logic (L)
Numeric (N)
Alphanumeric (A)
− <ETX> (End of transmission) = 0x03
− <CRC> = XOR of all characters subsequent to
<STX> and including the <ETX> terminator.
The value is hexadecimal coded and indicated
by two ASCII character.
The addressed SLAVE will respond with an
ANSWER whose structure depends from the
MESSAGE type.
When the MESSAGE is a reading command, the
SLAVE will respond transmitting a string with the
same structure of the MESSAGE.
Some error settings are foreseen:
0x15 NACK
0x32 UNKNOWN WINDOW
0x33 BAD DATA TYPE
0x34 OUT OF RANGE
0x35 BAD OPERATION
Using the RS 485 interface, the message structure
remains identical to the one used for the RS 232
interface, the only difference being that the value
assigned to the ADDRESS <ADDR>
77
TECHNICAL INFORMATION
FIELD
VALID
LENGTH
CHARACTERS
1
'0' = OFF
'1' = ON
6
'-', '.', '0' . . . '9' right
justified with '0'
10
from blank to '_' (ASCII)
NOTE
foreseen with
Read/Write com-
mands
foreseen only
with Write com-
mands
NOTE
87-900-968-01(C)
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