Interface ES128 to Robertson AP via NMEA 0183

I have a Robertson AP200DL autopilot manufactured around 1988 on my boat. This season I upgraded to an ES128 MFD along with radar and sonar.

The Robertson has a 2 wire NAV receiver connection, and supports NMEA 0183 XTE-mode, @ 4800
Messages APB, APA, XTE, RMB or XTR

I have connected:
The Yellow wire on the Robertson “NAV IN” to Yellow (positive) on ES128.
The Green wire on the Robertson “NAV RET” to Brown (Neg.) on ES128.
I believe this is correct to have the ES128 talking out port 1, and the Robertson listening.

What must I do on the ES128 to actually send messages out of port 1 at 4800 to the autopilot?

Thanks, Richard