OK After a LOT of pulling my hair out.......I have found that the ENTTEC API 70304 PDF file is wrong.
It states that to output your DMX values for your "Universe" as Start of message delimiter, hex 7E, followed by the Label to identify type of message (=6 for the DMX Universe), followed by Data Length LSB, then Data Length MSB, followed by the bytes for the DMX values by channel order, followed by the end of message delimiter, hex E7. This is incomplete as there is an extra byte required called the "startcode byte".
So the correct data stream is:
Hex 7E, followed by the Label to identify type of message (=6 for the DMX Universe), followed by Data Length LSB, then Data Length MSB, then startcode byte=00, followed by the bytes for the DMX values by channel order, followed by the end of message delimiter, hex E7. I have also found that you either output channels 1-256 or channels 1-512. No other number for the universe worked for me.
Here is the output to the virtual COM port for a 512 channel universe:
7E + 6 + 1 + 2 + 0 + 512 bytes (values for ch's 1-512) + E7
Hope this helps someone
Mark Insero
OK The DMX USB PRO on my Windows 11 PC shows up as a serial port (COM2). All I need is to output over DMX 2 bytes at a time, the channel number and the value. I assumed this should be really easy. Looks like you send to the serial port 7E followed by some "label value" of which I cannot figure out, followed by two bytes indicating the message length (in this case 2 bytes) LSB=2 then MSB=0, then the message (in this case 2 bytes) followed by E7. Seven bytes total, but it does not work. Can anyone help?
Mark