27
PROGRAMMING THE FS700
Communications
The FS700 LORAN Frequency Standard may be remotely programmed
via the GPIB (IEEE-488) interface. Any computer that supports this
interface may be used to program the FS700. All features of the
instrument may be controlled.
GPIB Communication
The FS700 supports the IEEE-488.1 (1978) interface standard. It also
supports the required common commands of the IEEE-488.2 (1987)
standard. The FS700's device address must be set before attempting
to communicate with the FS700 over the GPIB interface. The address
is set in the SETUP menu, and may be set between 0 and 30.
Front Panel LED's
The FS700 has two front panel status LEDs that assist in programming.
The ERR LED lights and an error message is displayed whenever an
error is detected, such as an illegal command, or a parameter out of
range. The REM LED is lit whenever the FS700 is in a remote state
(front panel locked out). The FS700 may be returned to the local state
(front panel active) by pressing the FIELD button.
Data Window
To help find program errors, the FS700 has an input data window which
displays the data the FS700 has received over the GPIB interface.
This window is displayed in the SETUP menu. The last 256 characters
received by the FS700 may be examined using the up and down arrow
keys. The character most recently received is marked by a rectangular
block character.
Command Syntax
Communications with the FS700 use ASCII characters. Commands
may be in either UPPER or lower case and may contain any number of
embedded space characters. A command to the FS700 consists of a
four character command mnemonic, arguments if necessary, and a
command terminator (linefeed <lf> or EOI). No command processing
occurs until a command terminator is received. Commands may
require one or more parameters. Multiple parameters are separated by
commas ",". Multiple commands may be sent on one command line by
separating them by semicolons ";".
There is no need to wait between commands. The FS700 has a 256
character input buffer and processes commands in the order received.
If the buffer fills up, the FS700 will hold off GPIB handshaking until the
buffer has been partially emptied by command processing. Similarly,
the FS700 has a 256 character output buffer to store output until the
host computer is ready to receive it. If the output buffer fills up, the
buffer is cleared and an error is reported. The input and output buffers
may be cleared with the GPIB Device Clear universal command.
The present value of a particular parameter may be determined by
querying the FS700 for its value. A query is formed by appending a
question mark "?" to the command mnemonic and omitting the desired
parameter from the command. If multiple queries are sent on one
