Transcript Original Sparrow

Original Sparrow
Power Bus (recycled junk house wire)
28.636 MHz Oscillator
256kx4 dynamic RAMs
XC4010 FPGA
resistor DACs
Composite Video Output
VIA modulator/mixer chip
missing from socket
Config Eprom
Power supply not shown (equally as attractive)
Original Sparrow
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Some limited success got me into working with FPGA’s. Almost all the parts with the exception of
the FPGA were from from my parts junk box. I wasn’t sure I wanted to work with them at all, so I
spent $50 to buy just a chip, and put together a circuit myself.
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Video output quality wasn’t very good. Although it did work, it was extremely noisey.
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I had a lot of trouble trying to get the processor to work at all; but I spent so much spare time at it,
that I decided to just scrap it, and buy a real $200 FPGA board instead. Then the Sparrow2
processor was underway.
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The FPGA was auto-loaded from the EPROM, and the EPROM also served to contain processor
code. In order to reconfig the FPGA I had to program the EPROM’s and swap them around all the
time.
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The low pin count dynamic RAMs don’t seem like a bad solution, for a small low speed memory.
For instance using page mode on a dynamic RAM on can read the data bits serially, and get by
with a single 256k x 4 or 1M x 1 dynamic RAM.
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All the address and data lines were shared between the config EPROM, program code EPROM
space, and dynamic RAMs. The complex address multplexing was handled in the FPGA. So that
both the EPROM and dynamic RAM addresses could share the same FPGA pins.