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Model 3455A
3-81. Status Byte Message. The status byte message is
output by the 3455A in response to a serial poll and in-
dicates, to the controller, the nature of a service request
message (SRQ) from the 3455A. The following is a list
of the basic status byte codes output by the 3455A:
Status Byte Code
Decimal Code
72
It is possible for more than one of the basic status byte
messages to be true. In this case the resulting status byte
code would be the combintation of the basic status byte
codes being output. As an example, the resulting code
for the combination of the syntax error and trigger too
fast messages would be ASCII character J decimal code
74. The following illustrates the status Byte message in-
dicating the purpose of each relevant ''bit''.
Data Ready - Indicates to the con-
troller that measurement data is
available.
Applies
to
DATA
READY Request feature.
Syntax Error - Indicates improper
program
code.
Example
- Pro-
gram Code '"'F7" would cause a
syntax
error
since
the FUNC-
TION program set is only defined
for codes Fi through F6.
BINARY FUNCTION Error - In-
dicates improper BINARY
PRO-
GRAM code or incomplete binary
message. Similar to syntax error.
Trigger too Fast - Indicates the
3455A
has been
triggered
while
measurement data is being output
to the bus. Warns of possible in-
correct measurement information.
STATUS BYTE MESSAGE
bg
b7 bo
bs
ba
b3
b2
by
HOBO
Service Request if
DATA READY
(SRQ)
SYNTAX ERROR
BINARY FUNCTION
ERROR
bits 5 and 6 set high
TRIGGER TOO FAST
NOTE
All "bits" are low true; bit 8 is not used.
Section IIE
3-82. DATA OUTPUT CHARACTERISTICS.
3-83.
The protocol used by the 3455A
to output
measurement data must be followed in order to preserve
proper
data transfer over the HP-IB,
the following
notes on data transfer over the HP-IB may be helpful:
a. If a reading has been taken and thus resides in the
output buffer, the buffer is not considered busy until
the output handshaking begins. Thus, a new trigger will
indicate a measurement and the new reading will replace
the old reading. The old reading is lost.and there is no
SRQ condition.
b. Once the first character of measurement data has
been handshaken out, the buffer is considered busy un-
til one of the following occurs:
1. The balance of the reading is handshaken out.
2. "'Device'' or ''Selected Device'' clear is given.
3. The
3455A
power
is interrupted,
triggering
while the buffer
is busy will lose the new
reading and cause a ''Trigger too Fast'? SRQ
condition.
c. When
triggering and taking measurements
in a
loop, sufficient time must be allowed for the 3455A to
perform the entire A-To-D measurement cycle and buf-
fer data to become available after the first reading. The
'Wait'? statements in many 9800 series calculators are
convenient methods to avoid outputting the previous
buffer contents. This condition shows up as being ''One
reading behind'' in your measurement sequence.
d. If you know the output buffer is not busy, but
don't know whether it is full or not, sending a ''device''
or selected device'' clear followed by reprogramming
the desired conditions is a safe way to clear the output
buffer.
3-84. Bail Out Message.
3-85. Abort. The
Abort
message
unconditionally
ter-
minates all Bus communications and returns control to
the system controller. Only the system controller can
send the Abort message. Refer to the Operating Manual
of the controller being used for instructions on sending
the Abort Message.
3-86. instrument Measurement Times (Remote Contra).
3-87. In the Remote Operating mode, the 3455A takes a
certain amount of time to respond to a trigger message.
The overall time depends on the range, function, and
particular controller used. This time may also vary from
instrument to instrument. Table 3-6 gives the typical
measurement times, using the HP-IB. These times are
not part of the operating specifications of the instru-
3-13
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Troubleshooting
