I've said it before and I'll say it again.....back in
the 70s and early 80s people got really creative with their machines! In those
days if you needed a new peripheral or circuit board and one wasn't available
you designed and built it yourself. Take this one - a humble singleboard Microtan65
that's been lovingly enhanced by its owner, first by adding the TANEX ROM/RAM/serial
expansion on a twin-slot backplane and then an external and apparently rare
TUG Board E.S.C that had been produced by the Tangerine User Group to add a load of
extra ROMs. Of course, it HAD to be external since there wasn't space inside
that solid wooden box for a 3 slot backplane :) Also, the only options available were 2-slot and 12-slot.
The E.S.C (EPROM Storage Card) could hold up to 16 2716 ROMs and is controlled by a pair of
6821 PIA chips. Unfortunately there's zero documentation for the ESC but there IS for the followup board, which was
called the ESC COMBO. The manual gives each ROM slot's address so here's what's in my ESC:
$1000-$1FFF Word Processor
$4000-$47FF TUG Programmer's Toolkit
$4800-$5FFF TUG Xmas 'Parcel Post' game
Each ROM is loaded into RAM by a routine at $EFFC so to load it you type GEFFC
and the routine asks for ROM start address, length and RAM location to write to, so to load Invaders you'd type:
The machine will respond with EFFF meaning it's loaded, so to start the code
you'd type G400. Instant Invaders, in this case.
There's also a blinkenlights panel connected to a serial port and 2 more ports taking up the EPROM burner you can see in the pix - 3 9V batteries required! Finally there's a choice of either the original Tangerine hex keypad or a nicely cased 'real' keyboard that's been nicked from an original Bell&Howell Apple ][....
(For my ultimate in homebrew machines have a look at the Ohio Superboard at the bottom of this page)