Instruction manual

The first byte of a command is always 0xaa and the second byte is the address of the power supply.
The address should be set to 0. The third byte identifies the command "set to remote" and the
fourth byte is a 1, which means enable remote mode. If the fourth byte was 0, this command would
set the power supply to local mode.
The third byte of the response string is 0x12, which means this is a packet that gives the status of
the last command sent. The fourth byte is 0x80, which means the command completed
successfully.
On the power supply, you should see the Rmt annunciator turned on immediately after running the
script. You will also see the Link annunciator light up while communications are going on, then
blink out after a few seconds.
Press Shift + Local to return the power supply to local mode.
We've learned two key things about the power supply:
1. Commands are always sent as 26 byte packets.
2. For any command you send to the power supply, you must also request the return of a 26
byte packet. This returned packet will either be a status packet or contain the information
which you requested -- for example, the power level currently set.
Get in the habit of looking at the LEDs on the IT-E131 or IT-E132 interfaces. Every command you
send to the power supply should result in both the RX and TX LEDs blinking once. If this doesn't
happen, something is wrong with the code, interface, or instrument.
If you peruse the power supply manual's programming section, you can see it will be tedious to
construct all the commands as we did above. It would be a time saver to have a library do the low-
level byte and bit manipulations for us. This was the rationale for developing the ps178x.py
module.
B&K 1785, 1786B, 1787B, 1788 Python Library 15 January 2009 Page 5 of 14