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TTI-7 Iss.02 – 06/11
Command Syntax
Most command keywords have both a long and short form. The bus controller can send commands in either form
and also in any combination of upper and lower case characters. Instrument responses, however, are always in the
short form, upper case.
Data Types
The bus controller can also send data in a range of formats, but the instrument always responds in a precise format.
There are four principal data types:
Numeric Parameters
are decimal numbers which include an optional sign, mantissa, decimal point and exponent.
Engineering suffix units are not accepted. Ver 4.0 does not accept numeric parameters.
Discrete Parameters
have limited values e.g. SINGle, INFinite, and like command keywords they can have long and
short forms, upper and lower case.
Boolean Parameters
have a single binary value. The controller can send OFF or 0, ON or 1, but the instrument
response is always 0 or 1.
String Parameters
contain ASCII characters which are placed between a pair of double quotation marks, i.e. “ “.
Output Data Format
Non-reading queries
<80 ASCII character string
Reading queries
IEEE
SDDDD.DDD <lf>
RS-232
SDDDD.DDD <cr><lf>
Talk-only format
IEEE
ChA: SDDDD.DDD degC <lf>
(or F, K)
RS-232
ChA: SDDDD.DDD degC <cr><lf> (or F, K)
Where
S = sign (+/-)
D = decimal digit (0-9)
<cr> = carriage return character
<lf> = linefeed character
The resolution and units will be as set by the last manual or bus commands.
Note: In IEEE mode the EOI line is also asserted with the transmission of the <lf> terminator.
Input Message Terminators
In RS-232 mode, all messages sent to the instrument must terminate with either a <lf> character or a <cr>
character. It is also permitted to send both <cr><lf> to terminate a message; the <lf> is ignored.
For IEEE-488 mode, messages can be terminated in one of two ways:
- by sending a <lf> character at the end of the message
- by asserting the EOI line with the last character sent
It is also permitted to combine these, and assert EOI when sending the <lf> character.
Message termination always forces the command path back to the root-level ready for the next command message.
