Further issues with UART comms across Maxim SerDes GMSL Link MAX96705 MAX96706

[tbw2]

Further to this post: https://www.eevblog.com/forum/microcontrollers/pic16-uart-to-analog-devices-max96706-gmsl-chip-(serdes)-comms-issues/

Working:

• Comms between the PIC and MAX96706 (Deserializer), I am able to read & write to the registers OK.
• Link between both sides, parallel data from a row of switches is being sent from the MAX96705 (Serializer) across the coax into the Des chip, decoded, and displayed on LEDs.
• GPI/GPO pin is able to send the pin state of GPI (Des side) to the GPO (Ser side).

Not working:

• No ACK is being received by the PIC when addressing the Serializer via UART. example message 0x79, 0x81, 0x04, 0x01....... no reply

Investigated:

• Confirmed High Immunity mode is set Low on both ends.
• Cable length is 1mtr coax, signal integrity is expected to be ok.
• MS/HVEN mode is confirmed to be Base mode for both sides. This is checked by toggling MS at Des side, and nothing appears on TX/RS pins at Ser side.
• LCCEN is pulled high, setting Ser side TX/RX pins to UART output.
• Des register 0xCB says Control channel is NOT LOCKED. Unsure why. (reads 0x7B)

Am I badly mistaken, and comms is actually NOT possible between Des and Ser sides whilst the link is active?

Deserializer datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX96706.pdf
Serializer datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX96705.pdf

Thank you for reading.

[tbw2]

I had mistakenly set the CONF0 and CONF1 jumpers on the Serializer side incorrectly.

To make the UART Control-Channel work, I2CSEL needs to be set to 0, which can be achieved by:

CONF1=LOW, CONF0=MID

Which works for my setup which is using CXTP=1 for Coax Output