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As you can see, this one is built with
all wires under the board, leaving the compnent side looking nice and
clean. I was using regular 30AWG kynar insulated wire-wrap wire for interconnects
after routing GND and VCC with thicker wire from phone cable. ISA interface
is built using 8255 for extra control and address wires, pair of 74374's
for capturing high byte of 16-bit data bus, and some glue logic for bus
timings. 8052 MCU runs a bit overclocked from 14.31818 MHz which is and
OSC frequency on ISA; ISA bus clock is OSC/2. The keyboard interface socket
is empty, but is meant for PIC16F84, running at OSC/4. PIC will talk to
keyboard, decode keystrokes to ASCII, and make them available in parallel
form via one of the 8255 ports. I plan to fill the empty sport at the
bottom of the image with 8-pin RTC either from Dallas or Philips, whichever
I get first. Ideally, I will convert all the glue logic to Xilinx CPLD,
leaving only MCU, MAX232, RAM/ROM, 8255, and PIC to surround it. Most
of this stuff is experimental anyway, and you can freely leave out modules
you don't need, if the high chip count makes you dizzy. I have currently
tested it with 8-bit ISA COM port card, and was able to successfully send
data via UART on it, so the principle works. I plan to build VT100 terminal
out of this prototype, PC keyboard, VGA card, and monitor.
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