We Have a PCB Now!

So when you consider yourself a designer, from a hardware perspective especially, you will have to make decisions that are not directly driven by your project's goals but rather by some production costs constraints. This is the voice of reason and it is what your boss wants to hear, obviously.

 

Z79Forth is not a professional product development effort in any modern way. It is a neo-retro endeavor. What this means is that I stayed away from contemporary packaging technology--namely SMT, which I think is not to be considered in scope for the amateur market. Deliberate choices were made at various points in time during the hardware development phase of the project. I think a few of them are worth elaborating on:

• use of through-hole only TI's HCT technology. This will get you TTL level compatible inputs, CMOS level compatible outputs and low power consumption, the whole thing under adequate switching times for old times' clock frequencies.
• use of CXO integrated oscillators. Those beat quartz based circuitry from an economical standpoint. They are compact (DIP8) and easy to integrate to a board.
  
• use of CompactFlash technology for mass storage. This used to be an exotic field accessible only to corporations wealthy enough to buy the standard specifications. This is no longer true since anyone is now enabled to retrieve the CF specifications from the Internet.
• use of an ATA/CF adapter. The device itself can be purchased from Eastern Asia sources at a decent cost. The true value of this particular item, in the context of the 2.2 schematics' BOM, cannot publicly be stated because it is based on a leaked proprietary document.
• use of an FTDI USB serial adapter. The thing just works and supplies power to the board. Z79Forth uses a module sold by az-delivery (Germany based).
• flexible USB/RS232 jumper based multiplexer. Uebercool stuff! It relies on an a Maxim Integrated MAX232 pump charged based converter. RS232 output might be routed to an IDC-10 connector (DTE) or to USB.

The overall design was made to be flexible enough but not up to the point where the board could not be configured by experts only. Easy of use and simplicity always were central concerns of mine.