October 1, 2018
Is it permissible to use both the front and rear connectors of Port A-H simultaneously on Octo 6405?
SCOPE: Applies only to Octos with DMX/RDM ports on front and rear
The short answer is "NO". The front and rear ports are a convenience to the master electricians so they lay out their dimmer beach with cable picks landing in front or behind the racks; not both. For each of Port A through H, use one and only one port. It is permissible to have Port A connect to the front and Port B out the rear. There is no software configuration necessary; both ports are hot all the time.
Why does this matter?
Properly installed DMX runs have terminators at both ends. Typically, electricians are used to installing an XLR terminator at the end of the chain, but what some may not realize is that almost all consoles and gateways have a similar 120-ohm terminator at the source. Two per line; no more, no less. If you were to run out both the front and back of the 6405 and terminate both ends, the link would have three terminators which is not valid. If you only terminated the front link, the rear link would be non-compliant and could cause reflections. Note: It is not necessary to terminate the unused ports on the device itself as the traces inside are very short.