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Section IV-C: Operating the SP-750i Using a Computer
The Acton SP-750i Monochromator can be controlled from an RS232 terminal or computer using
RS232 or IEEE488. The same command set, listed below, is used for both RS232 and IEEE488.
Commands can be sent as single commands or grouped in strings of commands. All commands are single
words (contain no spaces) and all commands in a string are separated by at least one space. Parameters, if
needed, precede the command and are separated from the command by at least one space (e.g. 546.7
GOTO).
For RS232 operation, the port set-up is 9600 baud, 8 data bits, 1 stop bit and no parity. All commands or
strings of commands must be terminated with a carriage return (0D hex). The SP-750i responds to a
command when the command has been completed by returning the characters OK followed by carriage
return and line feed (hex ASCII sequence 20 6F 6B 0D 0A). The default condition is to echo each character
that is sent to the SP-750i.
When using the IEEE488 (or GPIB) interface, the default device address is 11. The device address can be
set to any value from 1 to 30 using the command SET-ID. The command ?ID is used to read back the IEEE
address. Each command or string of commands must be terminated with a carriage return (0D hex). When
sending a command or string of commands, it is important to wait for the monochromator to complete the
processing of that command string before sending another command. This is accomplished by checking the
status byte. The monochromator controls bits in the IEEE488 status byte which can be read from the
IEEE488 controller. The command for reading this status byte will be unique to your IEEE controller.
For example, with National Instrument controllers, the command is IBRSP. With CEC controllers, the
command is SPOLL.
IEEE488 Status Byte Bits:
Bit 0 0 = command is being processed
1 = SP-750i ready for another command
Bit 1 0 = no errors
1 = SP-750i detected an error in the command
Bit 7 0 = no response or response has been read
1 = SP-750i generated a response which is now ready to be sent
Note that with some fast computers, it is necessary to add a few milliseconds delay in your program after
sending a command and before checking the status byte to allow time for the status byte to be updated.
Monochromator Wavelength Movement Commands:
GOTO Goes to a destination wavelength at maximum motor speed. Accepts destination
wavelength in nm as a floating point number with up to 3 digits after the decimal
point or whole number wavelength with no decimal point.
<GOTO> Same as GOTO (For compatibility with software written for previous Acton SP
models.)
NM Goes to a destination wavelength at constant nm/min rate specified by last NM/MIN
command. Accepts destination wavelength in nm as a floating point number with up
to 3 digits after the decimal point or whole number wavelength with no decimal point.
<NM> Same as NM (For compatibility with software written for previous Acton SP models.)
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