Varian PHD-4, Instruction Manual

Page: 35 / 41

TECHNICAL INFORMATION
30 87-900-120-01 (A)
RS 232 COMMUNICATION DESCRIPTION
The RS 232 interface is available on the connector
P2.
Communication Format
•
8 data bit
•
no parity
•
1 stop bit
•
baud rate: 600/1200/2400/4800/9600/19200
programmable
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
M CRC
to the controller (SLAVE);
2. the controller answer with an
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
corresponding ASCII character.
−
<STX>
(Start of transmission) = 0x02
−
<ADDR>
(Unit address) = 0x80 (for RS 232)
<ADDR>
(Unit address) = 0x80 + device
number (0 to 31) (for RS 485)
−
<WIN>
(Window) = a string of 3 numeric
character 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 FIELD
LENGTH
VALID
CHARACTERS
Logic (L) 1 ‘0’ = OFF
‘1’ = ON
Numeric (N) 6 ‘-‘, ‘.’, ‘0’ . . . ‘9’ right
justified with ‘0’
Alphanumeric (A) 10 from blank to ‘_’ (ASCII)
−
<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
.
NOTE
Some error settings are foreseen:
0x15 NACK
0x32 UNKNOWN WINDOW
foreseen with
Read/Write
commands
0x33 BAD DATA TYPE
0x34 OUT OF RANGE
0x35 BAD OPERATION
foreseen only with
Write commands