Control Techniques UD70, User Manual

Page: 67 / 154

UD70
Issue code: 70nu2
Serial communications 6-7
Data field
Data to be sent or requested occupies the characters immediately after the
parameter number. The minimum length of the data field within a message
structure is two characters.
The data is normally expressed as a decimal numeric value. Hexadecimal
format may also be used by specifying the first character of the data field as
a
X
.
The first character of the data field (
D1
) can be only one of the following:
Space (32 dec.)
+
–
X (for hex.) — hex. is typically used to access I/O Box data.
Block checksum (BCC)
In order to ensure that the messages from or to the
UD70
do not become
corrupted during transmission, all write messages and data responses are
terminated by the block checksum character (
BCC
). See Calculating the
block checksum (BCC) later in this section.
Reading parameters
To read a parameter, the following message is sent:
Control Address Parameter Control
EOT GA GA UA UA M1 M2 P1 P2 ENQ
Where:
GA
= Group Address
UA
= Unit Address
M1 M2
= Menu number
P1 P2
= Parameter number
Note
No
BCC
character is sent in this message.