Thorlabs APT protocol

A functional implementation of the Thorlabs APT protocol

Outgoing messages

Outgoing messages are python functions in the top level namespace. Each function has parameters relevant to the particular message, all messages have source and dest parameters. The function names are lower-cased from the names in the documentation and the "MGMSG_" has been omitted. These functions return bytes, they do not send the message over the transport layer

For example:

>>> import thorlabs_apt_protocol as apt
>>>
>>> apt.mot_move_home(source=1, dest=0x50 ,chan_ident=1)
b'C\x04\x01\x00P\x01'
>>> apt.mot_move_absolute(source=1, dest=0x50, chan_ident=1, position=2048)
b'S\x04\x06\x00\xd0\x01\x01\x00\x00\x08\x00\x00'

Incoming messages

Functions which allow for parsing bytes into dictionaries are also provided, but are not imported into the top level namespace by default. The recommended way of parsing is to use the provided Unpacker object.

This object takes a file-like object (such as a pyserial Serial instance) and provides a generator to parse the incomming messages. If no file object is provided, and internal BytesIO instance is used, and can be provided with bytes via the feed method. The generator yields namedtuple instances.

Usage with pyserial:

>>> import thorlabs_apt_protocol as apt
>>> import serial
>>>
>>> port = serial.Serial("/dev/ttyUSB0", 115200, rtscts=True, timeout=0.1)
>>> port.rts = True
>>> port.reset_input_buffer()
>>> port.reset_output_buffer()
>>> port.rts = False
>>> port.write(apt.hw_no_flash_programming(source=1, dest=0x50))
>>> unpacker = apt.Unpacker(port)
>>> for msg in unpacker:
...     print(msg)
...
>>>

On Windows, you must toggle a driver setting to make the COM port appear:

Within Device Manager, right click on the APT device (under USB devices), and go to Properties. On the Advanced tab, check the box that says Load VCP (VCP stands for Virtual COM Port). Unplug and replug the USB cable to make it load the COM Port.

If the Advanced tab does not appear, I was able to use FTDI's FT_PROG. With all other Thorlabs programs not running, click Devices > Scan for devices. Review over the provided ID information to ensure that you are editing the correct device, FTDI provides serial communication for many different devices from several manufacturers, it is very possible you have multiple devices which show up. Under the Hardware Specific, uncheck the Load D2XX box. This box is a bit of a misnomer, as it really means "Load only D2XX", as when unchecked the D2XX driver (which the Thorlabs provided programs use) is still loaded, but the VCP driver is also loaded. Click Devices > Program.

Upon reconnecting (unplug and replug USB) the Advanced tab should appear as above, but the Load VCP driver option may not be checked yet.