XT2640 Operating Manual
13 July 2016
Page 140 of 187
+1.2345678e6
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24.2.2.5
VDEF
COMMAND
FIELD
SYNTAX
This field type allows you to define a VPA using any one of the following syntaxes‐
1 to 3
NR1 syntax
A1 to A3
KEYWORD syntax
VPA1 to VPA3
KEYWORD syntax
CH1 to CH4
KEYWORD syntax, defines the VPA which is presently configured to use the channel identified by CH1 to
CH4; some commands do not support this syntax within a VDEF field
24.2.2.6
CDEF
COMMAND
FIELD
SYNTAX
This field type allows you to define a channel using any one of the following syntaxes‐
1 to 4
NR1 syntax
CH1 to CH4
KEYWORD syntax
24.2.2.7
RDEF
COMMAND
FIELD
SYNTAX
This field type contains 1 to 5 sub‐fields which define a measurement result to be used. See a later section for details regarding the
sub‐fields of the RDEF command field type.
24.2.2.8
DDEF
COMMAND
FIELD
SYNTAX
This field type contains 1 to 5 sub‐fields which define a measurement result to be used. See a later section for details regarding the
sub‐fields of the DDEF command field type.
24.2.2.9
COLOR
COMMAND
FIELD
SYNTAX
A COLOR command field contains three NR1 type sub‐fields defining the level of the red, green and blue color components
respectively. Each value is a maximum of 255 corresponding to full brightness of the respective color.
24.2.2.10
BLANK
COMMAND
FIELD
SYNTAX
In some cases it is allowed to have a blank command field. This is a field which has a preceding field separator character but is
immediately followed by another separator or terminator character. Except for a STRING command field, a blank field may contain
one or more whitespace characters but no other characters.
24.3
RESPONSES
TO
COMMANDS
Some commands cause the XT2640 to respond with a requested data response or set of data responses. The response is formed by a
set of fields, similar to those for commands described above.
Note that all command keywords which end with the ? character cause a response; all command keywords which do not end with the
? character do not cause a response.
All responses from the XT2640 use the standard 7‐bit ASCII character set using 8‐bit encoding (the 8
th
bit is zero) independent of the
actual interface being used.
You may request more than one response in a set of commands, in which case each response (or set of responses) is separated from
the previous by a comma separator and the responses are included in the same order as they were requested. A complete response
is always terminated by a carriage return followed by a line feed ASCII character and may contain up to 65535 characters in total.
It is expected that after a command is given to the unit to produce a response that the originator will not issue further commands
requesting a response until that prior response has been fully received. If the unit receives a command which requests a response
but the prior response has not been fully transmitted then this raises a Tx Overrun error.
24.3.1
RESPONSE
FIELDS
As defined for each such command a response is one or more fields, each of which is of the following types.
24.3.1.1
STRING
RESPONSE
FIELD
SYNTAX
A STRING response is a set of ASCII characters forming the response. Only printable ASCII characters are used and the length of a
STRING response is variable, the terminating comma (if more response fields follow it) or the terminating carriage return and line
feed characters should be used to determine the end of a STRING field.
24.3.1.2
NR1
RESPONSE
FIELD
SYNTAX
A NR1 response is a set of ASCII numeric characters defining an integer value. The length of a NR1 response is variable, the
terminating comma (if more response fields follow it) or the terminating carriage return and line feed characters should be used to
determine the end of a NR1 field. A NR1 response never includes a polarity symbol as all such responses are positive.
24.3.1.3
NR3
RESPONSE
FIELD
SYNTAX
A NR3 response is a set of ASCII characters defining a floating point numeric value. The length of a NR3 response is fixed at 11
characters however it is recommended that the terminating comma (if more response fields follow it) or the terminating carriage
return and line feed characters be used to determine the end of a NR3 field.
A NR3 response always has the following parts in the order shown –
A polarity character, defining the polarity of the numeric
