3-33
3
3.8.2.1 Configuring for a Talk String (Digital Inputs)
The SCPI CONFIGURE and FORMAT subsystems are used to configure
the digital interface for an input string before inputting data with string
commands. In Figure 3-3, bytes 2 and 3 are used to input 16 bits of data as
BCD/HEX characters from a digital panel meter (DPM). The DPM has a
2 1/2 digit output with a polarity signal and a conversion done signals The
data signals are positive true and the conversion signal is a high true BUSY
pulse. The DPM accepts a low true HOLD signal to inhibit future
conversions. The configuration commands are:
e.g.
CONFigure:INPut (@ 2,3)
'selects bytes 2 and 3
CONFigure:INPut:POL 1
'high true input data
CONFigure:INP:HAND ON
'enables input handshake
CONFigure:EDR 0
'for low going input when
BUSY ends
CONFigure:INH 0
'for low going INHIBIT output
to hold the DPM
Note that the above commands use the values recorded in Table 2-10 when
the example cable was designed.
The 4863 uses the DPM's polarity output signal to generate plus and minus
signs in the talk data string. The technique to do this is to jumper three of
the four input lines for a nibble so that the DPM's polarity signal will switch
between two values and therefore two characters in the Talk Translation
Table. In the example, the digital inputs are wired so the input code is 101P
with P being the DPM's Plus signal. When Plus is true, the input code is
1011 or a HEX B. When plus is false, the input code is 1010 or a HEX A.
The custom Talk Translation Table will include the ten numbers (0-9), and
replace the A and B characters with - and +. The characters " ., E" and a
space will be used to finish the table. The format commands then are:
e.g.
FORMat:TALK TABLE 'selects a custom conversion
FORMat:TALK:TRANS 0123,.E space
'specifies the custom table.
Note that space is a space character, not the letters s p a c e.
