18 Feb
2010
18 Feb
'10
1:19 a.m.
On Wed, Feb 17, 2010 at 13:49, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
The main problem is that those breadboard are
terrible. It's not the
clock speed that matters, it's the swtiching time of the IC. Most modern
ICs have ouptus that switch so fast that when you combine them with the
stray capacitances on the breadboard and the relatively high impedance
power connections, you get power and ground lines bouncing all over the
place. Without a _good_ 'scope it's impossible to know why your circuit
doesn't work. If you stick to 4000 series CMOS you'll be alright, but
modern 74xxx familes are pushing it. Really pushing it.
But if you're just learning high speed don't matter, even with full
computer prototypes. Incidentally, I just saw this:
http://blog.makezine.com/archive/2010/02/building_a_cpm_68k_computer_from_s…
Crazy, but I'm cheering for him! Retrotastic! :-)
Joe.
--
Joachim Thiemann :: http://www.tsp.ece.mcgill.ca/~jthiem