I got it to work on separate Arduino I will post step by step and add comment tomorrow I have get to bed for work tonight
No multiplexer just prototype shield and Arduino Mega 2560.
1) 5 volt from 2560 to VCC on stamp.
2) ground to ground
3) TX3 from 2560 to RX on stamp.
4) RX3 from 2560 to TX on stamp.
5) Connect USB to 2560.
open IDE>open file EZO Mega> keep BAUD rate the same (9600) for the first load of code> load code> open serial monitor> send this: serial,38400<cr> next in IDE change the SERIAL(9600) to SERIAL(38400) load new code to 2560 open the serial monitor change baud rate to 38400 and send this c,0 to stop constant read then send this (serial,?<cr>) response should be (?*OK,38400)
THIS WAS NOT DONE ON FERDUINO BOARD WAS ON A STAND ALONE 2560 AND PROTOTYPE SHIELD.
Happy reefing to all.