Control Techniques UD70, User Manual

Page: 65 / 154

UD70
Issue code: 70nu2
Serial communications 6-5
The character set used is called the low
ASCII
set. The set comprises 128
characters decimally numbered from 0 to 127. The first 32 characters in the
ASCII
set (hex. 00 to 1F) are used to represent special codes. These are the
control codes, each of which has a particular meaning (eg. start of text is
called
STX
and is
ASCII
code 02.)
On a computer or terminal, the
STX
character may be transmitted by
pressing Ctrl Ctrl+B B. When the
UD70
is in standard
ANSI
mode, it recognizes
that a command follows the
STX
character.
The control code
EOT
(end of transmission) instructs all
UD70
cards and
Drives on the
RS485
bus to be ready to receive a new message — it is often
sent at the start of a message so that all the devices are set at Ready to Ready to
receive message receive message.
Control characters
Commands and requests are sent in message packets. Each message is
started with a special control character, and may contain control characters.
A list of all the control characters that can be used when sending a message,
and receiving is as follows:
Character Meaning ASCII code
(decimal)
Keyed as...
EOT Reset
Instructs the UD70 to prepare for a new message.
Also indicates parameter does not exist.
04 Ctrl D
ENQ Enquiry
Used when interrogating.
05 Ctrl E
STX Start of text
Used to start a command.
02 Ctrl B
ETX End of text
Used at the end of a command.
03 Ctrl C
ACK Acknowledge (message accepted) 06 Ctrl F
NAK Negative acknowledge (message not understood) 21 Ctrl U
BS Backspace (go to previous parameter) 08 Ctrl H