TUTD Serial communications

Hi, first time posting, and I'll make the generic newbie posting.

I have a 2013 caprice ppv (9c1 so no TUTD shifter) and I noticed in the default tune that TUTD is set to serial, which had me wondering if it's controlled via the CAN network or it means serial communications with the tcm or bcm via something like UART. If it's can has any identified the PID's for shifting and modes? I know hardwiring to the tcm is better and probably has a faster response time, but it's a lot of work and vs programing a microcontroller on a can network to send those pids for shifting.

Cheers!
-chipperdoodles

Serial would be CAN based from the BCM. Hard wire would be a direct wire to the TCM