Much appreciated, as before, the 'manual' is not too explicit on anything, however, it supposes that I can 'simply' put in BCD data on serial in 4 bytes and the onboard MCU will read and display. Thus, I either need to make the handshake work, or, as you said, cut into the board and jump straight to the decoders using my Arduino to do the MUX and shift reg functions. I also will be outputting PWM for 12 steps for a graphical representation of digits, and using 2 more of these units as standalone power meter readings, which will also be interesting. Don't mean to sound ignorant, but I am a fast track newbie and wonder if I can do the BCD outputs or a duplex serial with the Mega for TX RX control serial, not completely sure of the capabilities. Am VERY looking forward to getting full into the applications that the Arduinos can do, as I have a million uses for them.. I have successfully hand built circuits CMOS and TTL that would have been a breeze had these little buggers been available 10 years ago. I will contact MFG and see if I can get some other answers, will see how that goes. thx again to all for your input. 10001110101.