GPIB OPERATION
3-2-5
Program data
Data can take many forms, as follows:
Decimal Numeric Data is a flexible numeric format which encompasses integer, fixed
point and floating point (mantissa and exponent) representations. Data is rounded to a resolution
appropriate to the function. Decimal data can, in most cases, be followed by the appropriate
units. If no units are present, the specified default units are assumed.
Character Data is an alphanumeric word.
String Data consists of a number of 7-bit ASCII characters enclosed in quotes, either a
pair of single ('ASCII 39') or double ("ASCII 34") quotes may be used.
Block Data is used by *PUD and allows a number of 8-bit bytes to be transferred. For
further information see the Service Manual.
Some commands can accept Multiple Data items which are separated by commas, for
example MODE FM,AM.
Message exchange protocol
The controller should not attempt to read a response until it has sent the entire query
message (terminated by EOM). Also, it should not start to send a new message until it has read
the entire response (terminated by EOM). The query message may contain more than one query
message unit, but only one response message (containing several response message units) is
generated.
Failure to follow the protocol will generate a query error:
UNTERMINATED (error 116) occurs when the controller attempts to read a response
without having sent a query.
INTERRUPTED (error 117) occurs when the controller starts to send a new message
before having read the response to a preceding query.
DEADLOCK (error 118) can only occur if the input and output buffers are both filled by
the controller having sent an extra long Message containing several query message units.
The NAV-750C have input buffer stores of 256 characters and an output buffer of two
response message units.
Remote/local operation
When the NAV-750C Signal Generator is addressed by the controller it will enter its
remote mode and the screen will have only one key legend,
[LOCAL].
Pressing this key returns
the unit to normal manual operation, unless Local Lockout has been asserted by the controller.
