2
1 INTRODUCTION
The C300 Series of controllers is extended
by the addition of a serial data
communication option which allows
addressing and reprogramming via a
computer terminal or host computer.
The RS422/485 communication standard is
used with the following logic levels:
a) for logic ‘1’ (MARK condition or IDLE
state) the ‘A’ terminal of the transmitter is
negative (0V) with respect to the ‘B’
terminal (+5V)
b) for logic ‘0’ (SPACE condition or ACTIVE
state) the ‘A’ terminal of the transmitter is
positive (+5V) with respect to the ‘B’
terminal (0V).
Parity is used for simple error checking. The
parity bit is a one-bit code which is
transmitted in addition to the ASCII
character. It can detect only one error per
character, since two errors may cancel out.
Parity is calculated by finding the sum of
logic ‘1’s in the character and either:
a) setting the parity bit to logic ‘1’ if the sum
is odd, or logic ‘0’ if the sum is even,
when using even parity
or
b) setting the parity bit to logic ‘0’ if the sum
is odd, or logic ‘1’ if the sum is even,
when using odd parity.
The block check character (BCC) is an
additional form of checking and is the
arithmetic sum of all the characters in a
complete message (excluding parity bits) –
see Appendix A3 on page 28. Error
detection is achieved by comparison of the
BCC’s of the transmitted and received
messages.
2 PREPARATION
The procedure is similar to that described in
the Operating Instructions (IM/C300) with
additions as detailed in this section.
2.1 Company Standard Settings
Only those parameters detailed on the
customer order are programmed at the
factory. If any parameters are unsuitable for
the application they can be reprogrammed –
see Section 7 of the Operating Instructions
(IM/C300). Serial data programming details
are to be found in Section 7 of this manual.
Standard parameter settings for the serial
data programme are as follows:
Instrument Identity 01
Parity odd parity
Block Check
Character (BCC) BCC on
Transmission Rate 9600 baud.
Instrument
Viewed
from Rear
Fig. 4.1 Serial Connections
8
9
10
11
12
Common
Rx+
Rx–
Tx+
Tx–
ABC
C
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