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2620A, 2625A
Users Manual
4-14
Input Strings
The instrument processes and executes valid input strings sent by the host. A valid input
string is one or more syntactically correct commands, separated by semicolons (;),
followed by an input terminator. ASCII and IEEE-488 bus codes are provided in
Appendix B.
The instrument stores received input in a 350-byte input buffer.
Note
Input strings received over the RS-232 interface are not executed or
checked for proper syntax until an input terminator is received. If the RS-
232 input buffer becomes full, a Device Dependent Error prompt is
returned, and the input string is ignored.
The instrument accepts alphabetic characters in either upper- or lower-case. If a
command cannot be understood (i.e, the equivalent of an IEEE-488 "Command Error"),
the command and the rest of the command line are ignored.
Input Terminators
An input terminator is a character or command (IEEE-488.1), sent by the host, that
identifies the end of a string of one or more commands.
When an input terminator is received (RS-232 applications), the instrument executes all
commands entered since the last terminator was received, on a first-in, first-out basis. (In
IEEE-488 applications, commands are not delayed until receipt of an input terminator;
commands are executed as they are received.)
As input characters are processed and commands executed, space is made available in
the input buffer for new characters. In RS-232 applications, if a communications error
(e.g., parity, framing, overrun) is detected or the input buffer fills, a device-dependent
error is generated. If the input buffer is full, new characters are ignored as the instrument
waits for a termination character.
If, on the other hand, the input buffer becomes full when the IEEE-488 interface is used,
the instrument stops accepting characters until there is room in the buffer. Characters in
the input buffer cannot be overwritten with the IEEE-488 interface.
The following are valid terminators for the RS-232 interface:
• LF (Line Feed)
• CR (Carriage Return)
• CR LF
• LF CR
The following are valid terminators for the IEEE-488 interface:
• EOI (End or Identity) on any character
• LF (Line Feed)
In some instances, a terminator is automatically transmitted by the host at the end of the
command string (i.e., the instrument’s input string). For example, in Fluke BASIC, the
PRINT statement finishes with a CR LF pair.
Typical Input Strings
Example strings that could be sent to the instrument over either IEEE-488 interface are
shown in Figure 4-3.