Fluke 8845A - How the Meter Processes Input; Input Strings; Input Terminators

8845A/8846A
Programmers Manual
18
How the Meter Processes Input
The following paragraphs summarize how the Meter processes input that is received from a
host or stand-alone terminal.
Note
In this manual input means a string sent to the Meter from a host. Output means a string
sent from the meter through the computer interface to the host.
Input Strings
The meter processes and executes valid input strings sent by the host. A valid input string
is one or more syntactically correct commands followed by an input terminator.
When the meter receives input, it stores it 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 or the input
buffer becomes full.
The Meter 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 remainder
of the command line is ignored.
Input Terminators
An input terminator is a character or command (IEEE 488.1) sent by the host that identi-
fies the end of a string.
In RS-232 applications, when the Meter receives an input terminator, it executes all com-
mands entered since the last terminator was received on a first-in, first-out basis.
As input characters are processed and executed, space is made available in the input
buffer for new characters. In RS-232 applications, if a communications error (e.g., parity,
framing, over-run) is detected, a device-dependent error is generated, and the input string
discarded. If the Meter's input buffer becomes full when it is used with the RS-232
interface, a device-dependent error is generated (see "Event Status and Event Status
Enable Register"), and the input string is discarded. If, on the other hand, the input buffer
becomes full when the IEEE 488 interface is used, the Meter stops accepting characters
until there is room in the buffer. Characters in the input buffer cannot be over-written
with the IEEE 488 interface.
Valid terminators for the RS-232 interface are:
• LF (Line Feed)
• CR (Carriage Return)
• CR LF (Carriage Return/ Line Feed)
Valid terminators for the IEEE 488 interface are:
• EOI (End or Identity) on any character
• LF (Line Feed)
In some instances, a terminator is automatically transmitted at the end of the host's output
string (i.e., the Meter's input string). For example, in Fluke BASIC, the PRINT statement
finishes with a CR LF pair.