I have been working on this as well. Here is some source code for sending strings through the serial port, although I wrote this for an RJ2, V5.22. I think it should work though...
PROGRAM ggg
%COMMENT = 'Serial Test 6'
VAR
file_var :FILE
text :STRING[8]
a_num :INTEGER
BEGIN -- serial test 6
-- Force User Screen
FORCE_SPMENU(tp_panel, SPI_TPUSER, 1)
-- Clear User Screen
WRITE TPDISPLAY(cr,cr,cr,cr,cr,cr,cr,cr,cr,cr,cr,'Opening Serial Port',cr)
-- Open serial port on User Operator Pannel
-- |------------- set to READ and WRITE
-- V V----- set to serial port on User Operator Panel
OPEN FILE file_var('RW','P2:')
-- Status messages
text = 'test'
a_num = 930
-- Write text to serial port
WRITE file_var ('test',cr)
-- Close serial port on User Operator Pannel
CLOSE FILE file_var
-- Write message on User Screen
WRITE TPDISPLAY('TASK COMPLETED

',cr)
END ggg
~~~ FnA Robot Guy
(Fanuc and Abb robot Guru)