Keithley 6512, Instruction Manual, Page: 79 / 156

IEEE-488 Programming
3-24
3.6.1 Bus error
A bus error will occur if the instrument receives a device-de-
pendent command when it is not in remote, or if an illegal de-
vice-dependent command (IDDC) or illegal device-
dependent command option (IDDCO) is sent to the instru-
ment. Under these conditions, the complete command string
will be rejected, and the following message will be dis-
played:
b Err
In addition, the error bit and pertinent bits in the U1 word
will be set (paragraphs 3.2.13 and 3.2.16), and the instrument
can be programmed to generate an SRQ under these condi-
tions (paragraph 3.2.13).
No Remote error
A no remote error can occur when a command is sent to the
instrument when the REN line is false. Note that the state of
REN is only tested when the X character is received.
IDDC error
An IDDC error can occur when an invalid command such as
H1X is transmitted (this command is invalid because the in-
strument has no command associated with that letter).
IDDCO error
Similarly, an IDDCO error occurs when an invalid option is
sent with a valid command. For example, the command T9X
has an invalid option because instrument has no such trigger
mode.
3.6.2 Number error
A number error occurs when an out of range calibration com-
mand (A) value is sent to the instrument. Under these condi-
tions, the instrument will display the following error
message:
n Err
The command string will be accepted, but the calibration val-
ue will remain unchanged.
3.6.3 Trigger overrun error
A trigger overrun error occurs when the instrument receives
a trigger while it is still processing a reading from a previous
trigger. Note that only the overrun triggers are ignored and
will have no effect on the instrument except to generate the
message below. When a trigger overrun occurs, the following
front panel message will be displayed for approximately one
second:
t Err
3.7 Bus data transmission times
A primary consideration is the length of time it takes to ob-
tain a reading once the instrument is triggered to make a con-
version. The length of time will vary somewhat depending
on the selected function and trigger mode. Table 3-4 gives
typical times.
NOTES:
1. Conditions: Input is on range, and times may depend on controller
used.
2. Preamp settling time (to 12%) is 2 seconds on preamp ranges (2, 20,
200pA), and must be taken into account by the user.
3. Volt time/error also applies to external feedback.
Table 3-4
Trigger to reading-ready times
Configuration
Time
(msec) Error (1% of
step input)
2V, 20V, 200V
200mV
20nA, 200nA, 20µA,
200µA, 20mA
20pA, 200pA
2nA, 2µA, 2mA
2pA
2nC, 20nC
200pC
20k
Ω
-200G
Ω
2k
Ω
365
780
365
365
780
780
365
780
365
780
0.01
0.1
0.01
55
2
0.1
25
2
0.01
0.1
0.01
0.1