Keithley 6221 User Manual

10-16 Remote Operations Model 6220/6221 Reference Manual
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In each of the above program messages, the path pointer starts at the root com-
mand (
:stat) and moves down the command levels until the command is exe-
cuted.
Multiple command messages
You can send multiple command messages in the same program message as
long as they are separated by semicolons (;). The following is an example showing
two commands in one program message:
:stat:oper; :stat:oper:enab <NRf>
When the above is sent, the first command word is recognized as the root com-
mand (:stat). When the next colon is detected, the path pointer moves down to the
next command level and executes the command. When the path pointer sees the
colon after the semicolon (;), it resets back to the root level and starts over.
Commands that are on the same command level can be executed without retyping
the entire command path. Example:
:stat:oper:enab <NRf>; enab?
After the first command (:enab) is executed, the path pointer is at the third com-
mand level in the structure. Since
:enab? is also on the third level, it can be
entered without repeating the entire path name. Notice that the leading colon for
:enab? is not included in the program message. If a colon were included, the path
pointer would reset to the root level and expect a root command. Since
:enab? is
not a root command, an error would occur.
Command path rules
• Each new program message must begin with the root command, unless it is
optional. If the root is optional, treat a command word on the next level as
the root.
• The colon (:) at the beginning of a program message is optional and need
not be used.
:stat:pres = stat:pres
• When the path pointer detects a colon (:), it moves down to the next com-
mand level. An exception is when the path pointer detects a semicolon (;),
which is used to separate commands within the program message.
• When the path pointer detects a colon (:) that immediately follows a semi-
colon (;), it resets to the root level.
• The path pointer can only move down. It cannot be moved up a level. Exe-
cuting a command at a higher level requires that you start over at the root
command.
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Keithley 6221 Specifications

General

Interface	GPIB, RS-232
Communication Interface	GPIB, RS-232
Current Sourcing Accuracy	±(0.03% of output + 20 pA)
Current Sinking Accuracy	±(0.03% of output + 20 pA)
Output Resolution	100 fA
Output Accuracy	±(0.03% of output + 20 pA)
Power Requirements	100 V to 240 V AC, 50/60 Hz