LeCroy 9400A Manual page 138

TIME/DIV ? This legal command generates a response message which
should be read by the host computer. In addition, the
MESSAGE READY bit is set in STB i. Because this bit is not
demasked, it does not generate a Service Request. However,
if STB I were now read with "STB I,?", the binary value
I0000000 (= 80 in hexadecimal or = 128 in decimal) would
be read, and this bit would be cleared.
Overload I This event, internal to the 9400A (but due to too large
signal at input 1 with 50 Q coupling), sets the OVERLOAD1
bit of STB 4. Since this bit is demasked, the INTERNAL
STATE CHANGE bit of STB 1 is also set. And because this
bit is also demasked, the RQS bit is set and the Service
Request is generated. If set to the default string, it
consists of sending 1 bell character (decimal 7), followed
by the carriage return character (default value of <END>),
via RS-232-C to the host computer.
AAA?
This illegal command generates a syntax error, and sets
the ERROR byte (STB 6) to the value ii. Since this byte
demasked, the ERROR bit in STB I is also set. And because
this bit is also demasked, it should also set the RQS bit
and generate a Service Request. However, it cannot since
it is already pending.
If the host computer reads the Main Status byte with the command "STB
i,?" at this moment, it will read the binary value llll0000, coded as
the decimal value 240 = 128+64+32+16. The Main Status Byte (STB i) acts
as an accumulator of all condition bits. Thus several bits are set.
After reading STB i, all bits will be cleared and no more Service
Requests are generated until some new event occurs.
7-56
Remote Operations