Step 6 : Power & IDE ribbon cables

I chose an AT class PC power supply for my prototype. They are lots of them available as junk, from older PC's and they are easier to switch on/off than ATX class (soft switch) power supplies. A lighted AC power switch from a dead coffee pot makes a nice touch also. Power to the boards is via the power supply disk drive connectors, which can be multipled via a "Y" cable assembly to additional boards. +5VDC and +12VDC is provided by the connector, however the unit only requires +5 for operation. A suitable ribbon bus can be had by taking an existing 40 (NOT the newer 80 conductor) conductor IDE ribbon cable, and adding additional crimp on connectors down it's length for additional boards. Try to keep the total bus length as short as possible to reduce the chance of data errors.

Step 7 : Programming

Easy as pie (or a piece of cake if you prefer).
As I mentioned earlier, only 4 instructions and 2 port addresses to deal with.
To transfer the Address to the controller address register, program writes the desired end address to Parallel Port BaseAddress +3.
To transfer the data pattern to the controller data register, the program writes the desired data to Parallel Port base address +4.
Execute: This is where we deviate from the standard EPP instructions Data Read and Address Read, and use either one of them to force the controller to process the Address / Data previously stored. By reading either Parallel port base address +3 or +4, we generate an internal controller Execute signal that outputs the stored address for translation by the register select / board select decoders, which is output to the IDE bus cable.
In the Output board, the appropriate board select lead is passed thru the dip switch to turn on the both bus receivers, which gates the data bits to the end register based on the active Register Select bit.

Step 8 : Cost

The chips used are relatively inexpensive, with most of them under $1 US each except for the 154 chip.
Due to the complex parallel busing used, the board design is somewhat of a challenge to do and was the most expensive part of the whole operation. Prototype bare PCB's ran me $60 US each. If you are into making your own PCB's, or want to wire wrap on a perf board, you can get your cost down, but it will take some effort.