20 Mar
2007
20 Mar
'07
5:48 p.m.
Jos Dreesen wrote:
I am currenly contemplating what kind of IO to put on
my coming i8008
system : what is it that makes blinkenlights (i.e. leds and switches )
seem so attractive ?
It must be about the worst possible way to interact with a computer...
So why is it then that almost all early micros had them ?
a 7segment display with keyboard ( as in a H8) is clearly more usable,
and would have cost nothing more. Or were early eproms (for the
monitor program) that expensive ?
Jos
If I recall the displays were put thru logic (7 segment for octal,
special for
hexadecimal) directly from the bus. Keyboards could be interfaced and
read by a monitor, but many had start and stop and step that were the
same as the bat switches. Proms were optional.
Proms could cost a lot. I recall paying retail prices of $20 for
2708's. The
distribution prices were pretty high, so adding a prom monitor was something
a low end system vendor wanted to avoid requiring.
The bat switch / led panel was the simplest, since it avoided having to have
a decoder on board, and used LED's, which were cheaper than early hex
displays. The systems that used octal (don't know of any kits, but saw
lots of home designs) could use a cheaper encoder, but hex displays were
not cheap, unless your rigged your own.
jim