Hi Ed,
If you're talking about the line WData = $00CC: GOSUB Send it's a command that makes the address pointer in the chip point at address 12 (which apparently is the Zoom register and makes the pointer increment automatically for each data write following the command. The mode register is at address 16 so, as far as I can see, it is being set to either $183E or $193E depending on which of the two subroutines are being called.

/Henrik.