Fluke 8842a User Manual download pdf (Page 62)

Remote Programming

INPUT SYNTAX

3-21

3-37. Definitions

• Output commands: Commands which load data into the output buffer. The output

commands are: the Get commands (G0 through G8); the Single-Trigger Command

(?); the Continuous Trigger command (T0); and Group Execute Trigger (GET), not to

be confused with the Get commands.

• Input terminator: An ASCII control code sent by the controller which tells the 8842A

to execute all device-dependent commands since the previous terminator.

Terminators are CR (Carriage Return), LF (Line Feed), EOI (End Or Identify), and

GET (Group Execute Trigger).

• Input command string: One or more device-dependent commands followed by a

terminator.

3-38. Input Processing

When the 8842A receives commands from the bus, it stores them in a 31-character input

buffer as a continuous string of characters. Commands in the input buffer are not

executed or checked for syntax until an input terminator is received or the input buffer

becomes full. The only valid input terminators are CR, LF, GET (Group Execute

Trigger), and/or EOI.

When the 8842A receives an input terminator, it executes the previous commands in the

order in which they were received. As input characters are processed and executed, space

is made available in the input buffer for new characters.

If the input buffer becomes full, the 8842A stops accepting characters from the bus until

all complete command strings currently in the input buffer have been executed. In this

way, characters sent to the 8842A are never lost due to buffer overflow.

In some instances, a terminator is automatically transmitted at the end of the controller’s

output string. For example, in Fluke BASIC, the PRINT statement always finishes with a

CR LF pair. If a controller does not have this feature, the programmer must transmit a

terminator explicitly.

The 8842A accepts alphabetic characters in either upper or lower case. Spaces, commas,

and control codes are ignored and are not placed in the input buffer. If the 8842A

receives a group of terminators (such as CR LF or CR LF EOI), only a single terminator

is loaded into the input buffer. Numeric values used in PUT commands may be in NR1,

NR2, or NR3 format as described in the IEEE-488 Codes and Formats Recommended

Practice. (These correspond to the signed integer, real number, and real-number-with-

exponent formats described under the N command.) For reference, Figure 3-8 shows how

the 8842A interprets messages.

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Fluke 8842a User Manual Page 62