UD78 User Guide
Issue code: 78nu2
A-2
Control characters
Commands and requests are sent in message packets. Each message is
started with a special control character, and may contain additional control
characters. A list of all the control characters that can be used when a
message is being sent or received is as follows:
Character Meaning ASCII code
(decimal)
Keyed as...
EOT Reset
Instructs the Drive to prepare for a new message.
Also indicates parameter does not exist.
04 Ctrl D
ENQ Enquiry
Used when interrogating the Drive.
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
Addressing
Each Drive on an
ANSI
communications bus must be given a unique identity
or
address
so that only the target Drive will respond to a command
transmitted by the system controller. The address comprises the following
two parts:
•
Group address (first digit)
•
Unit address (second digit)
Both the group address and unit address have a range of 1 to 9. A group or
unit address of 0 is not allowed (addresses 01, 10, 20, etc. are invalid). The
reason for this is that Drives can be grouped together (up to 9 units per
group), and a message can be sent over the
ANSI
communications bus to all
units of the group. To address a particular group, the unit address zero (0)
is used. For example, to address all units of group 6, the full address will be
60.
An additional feature is that a message can be sent to all units of all groups
simultaneously using the address 00. This address can be used to send a
Start command to a group of Drives which are mechanically coupled
together to drive a conveyer line. All the Drives will then start
simultaneously.