I have a Burgmaster VMC w/ 6M-b that has about 5k of memory and would like to try some 3d shapes but can't justify the grand the an over the counter BTR cost. I can up/download programs with Cadem but tape mode does nothing as far as the rs-232 goes. I would like to make a led array to feed the tape reader and opto for flow control.All input welcome no pun intended.

I once made the reverse, kinda, I used a older UART IC IM6402 to take the output from a tape reader (parallel) and convert to RS232, It should be possible to use an IC like this the other way around and input RS232 and convert to parallel data ( it has both transmit and recieve registers).
You would need to simulate the sprocket hole which is usually used for clocking the data, there should be a signal for this in a UART and also an input to simulate tape pause.
I believe the commercial ones also have an internal buffer.
Al

I plan on using the parallel port to do this. I have an old dos program called CNC File that will do this but the BTR that I had left with the old GE 550 control when I retrofited my HNC to an AH-HA pc control. I don't plan on using the drip feed very often as the rs-232 works for 95+% of what I make.

I found a interface card @ http://cnc4pc.com/Parallel_Port_Interface_Card.htm
that I think will be a big help with this project.