IEEE-488 Programming
3-18
Note that all returned values except for those associated with the terminator correspond to the pro-
grammed numeric values. For example, if the instrument is presently on the R3 range, the R bytes in the
status word will correspond to an ASCII 03. The returned terminator characters are derived by ORing
the actual terminator byte values with 30
H
. For example, a <CR> character has a decimal value of 13,
which equals 0D
H
. ORing this value with 30
H
yields 3D
H
, or 61
10
, which prints out as an ASCII equal
sign (=). This terminator conversion step is necessary to convert the standard terminators into display-
able form, as they will not normally print out on a computer CRT.
Error
The U1 command allows access to Model 6512 error conditions in a similar manner. Once the sequence
Conditions
U1X is sent, the instrument will transmit the error conditions with the format shown in Figure 3-4 the
next time it is addressed to talk in the normal manner. The error condition word will be sent only once
each time the U1 command is transmitted. Note that the error condition wor id actually a string of ASCII
characters representing binary bit positions. An error condition is also flagged in the status (serial poll)
byte, and the instrument can be programmed to generate an SRQ when an error condition occurs. (See
paragraph 3.2.8). Note that all bits in the error condition (U1) word and the status byte error bit will be
cleared when the U1 word is read. In addition, SRQ operation will be restored after an error condition by
reading U1.
Figure 3-4
U1 status (error condition) format
The various bits in the error condition word are described as follows:
IDDC—Set when an illegal device dependent command (IDDC) such as H1X is received (“H” is ille-
gal).
IDDCO—Set when an illegal device-dependent command option (IDDCO) such as T9X is received (“9”
is illegal).
No Remote—Set when a programming command is received when REN is false.
NOTE
The complete command string will be ignored if an IDDC, IDDCO or No Remote
error occurs.
6512
0/1
0/1
0/1
0
0/1
0/1
000
<CR LF>
MODEL
NUMBER
PREFIX
1 = IDDC
1 = IDDCO
1 = NO REMOTE
1 = TRIGGER OVERRUN
1 = NUMBER ERROR
ALWAYS
ZEROES
TERMINATOR
(DEFAULT
SHOWN)
Summary of Contents for 6512
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