Terminator - Keithley 776 Instruction Manual

IEEE-488 Operation
Table 4-7.
SRQ Mask Legal Co~nrnnnds
Bit Number B2 Bl
BO (LSB)
Reading
Command Error Done_ Ready
zf
NO NO
NO
NO NO
YES
:i
NO YES
NO
NO YES
YES
Q4 YES NO NO
::
YES NO YES
YES YES NO
Q7 YES YES YES
terminator may be changed
(see paragraph J-10-2). The
prefixes are listed in Table 4-9.
NOTES
1. The Error Status string will be returned only once
each time the command is sent. Once &xus is read. the
instrument will send its normal swing the next time the
instrument is addressed to talk and reading done bit is
set true.
2. To ensure that the correct status is received. the status
string should be read immediately after sending the
command. to avoid having an incorrect status transmit-
ted.
3. The status string should not be confused with the
status byte. The status string comains a string of bytes
pertaining to the various operating modes of the instro-
mew. The status byte is a single byte hat is read wilh
Table 4-8. Stntus Bvfe
Inferprcmtion
the SPE. SPD command sequence and contains informa-
tion on SRQ status.
4. The error status string is cleared by reading R7.
Reading this status also clears the reading done and lhe
error bits in the status byte.
4-l O-2. Terminator (2)
To allow a wide variety of controllers to be used. the
terminator can be changed by sending an appropriate
command over the bus. The default value is the com-
monly used carriage return, line feed (CR LF) sequence
(mode ZO). The terminalor sequence will assume this
default value after receiving a DCL or SDC.
The EOI line on the bus is usually set low by the
device during the last byte of its data transfer sequence.
In this way. the last byte is properly identified. allowing
variable length data words to be transmitted. The Model
776 will normally send EOl during the last byte of its
data string or status word. The terminator and the EOI
response from the Model 776 ma\ be sent with one of
the following commands:
ZO
= CR.LF with EOI
Zl
= CR.LF wilbout EOI
Z2
= LECR with EOI
23 = LF.CR without EOI
24 = CR with EOI
ZS
= CR without EOI
26 = LF with EOI
27
= LF without EOI
2% = No terminator with EOI
Z9
= No terminator without EOl
Interpretation Reading
0
"7s
0 0 0 Error Done Ready
4-16