Red Lion LEGEND - Manual (Page 36)

SENDING COMMANDS AND DATA (Cont’d)
If a unit has an address of zero, it will attempt to process any transmissions
from the other Legends as commands. These transmissions fill up the receive
buffer of the unit with an address of zero, which may produce unpredictable
results.
In a multiple unit configuration an asterisk must be sent to clear the input
buffer of all units on the line after a transmit value or print request command
is sent to a specific unit on the line. The Legend will require a maximum of 50
msec to process the asterisk (*).
The command string is constructed in a specific logical sequence. The
Legend will not accept command strings that do not follow this sequence.
Only one operation can be performed per command string. Below is the
procedure to be used when constructing a command string.
1. The first two or three characters of the command string must consist of the
Address Command (N) and the address number of the unit (1 99). If the
Legend address is zero, the address command and number need NOT be
sent.
2. The next character in the command string is the actual command that the
Legend is to perform (P, R, T, or V).
3. A Value Identifier is next if it pertains to the command. The command P
(print) does not require a Value Identifier.
4. The numerical data will be next in the command string if the “Change
Value” command is used.
5. All command strings must be terminated with an asterisk * (2AH). This
character indicates to the Legend that the command string is complete and
begins processing the command.
Below are some typical examples of properly constructed command
strings.
(EX. 1) Change Preset 1 Value to 123.4 on the Legend with an address of 2.
COMMAND STRING: N2VA1234*
(EX. 2) Transmit the Count Value of the Legend unit with an address of 3.
COMMAND STRING: N3TE*
(EX. 3) Reset Output 1 of the Legend unit with an address of 0.
COMMAND STRING: R1*
If illegal commands or characters are sent to the Legend, the unit will
respond by transmitting an error character “E” (45H) in which case the string
must be re transmitted.
When writing application programs in Basic, the transmission of spaces or
carriage return and line feed should be inhibited by using the semicolon
delimiter with the “PRINT” statement. The Legend will not accept a carriage
return or line feed as valid characters.
It is recommended that a “Transmit Value” command follow a “Change
Value” Command. If this is done, the reception of the data can provide a
timing reference for sending another command and will insure that the
change has occurred. When a “Change Value or Reset Value” command is
sent to the Legend, there is time required for the unit to process the command
string. The diagrams show the timing considerations that need to be made.
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