24 Apr
2007
24 Apr
'07
5:21 p.m.
Subject: Re: Hand-rolling a CP/M machine
From: "Ethan Dicks" <ethan.dicks at gmail.com>
Date: Tue, 24 Apr 2007 12:01:24 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On 4/24/07, Dave Dunfield <dave06a at dunfield.com> wrote:
I'm with you there.
Not bad at all, Three states and one is always 00h. Doesn't take much
to do that. The sequency you want is say "JMP FOOOH" or C3h, 00h, F0h
I think a pair of 74157s could encode that.
Another equally sneeky/sleezy trick was to force NOPs (00h) on the buss
till you hit the rom address where you disable the force nop logic.
That's slow (takes 61.4mS at 4mhz) though.
Allison
Allison
The point
of ROM vs RAM at $0000 has been gone over a few times. Do
"standard" CP/M machines use a shadow-ROM technique, or what, to
cold-start?
There are many ways to accomplish getting RAM at 0, even though the CPU
has to boot from there. Some systems force a JMP instruction onto the BUS
during the first three
fetches, which transfers control to a ROM at a higher location.
That seems like it would take a bit of extra circuitry to do. 
24 Apr
24 Apr
8:13 p.m.
On Tue, 2007-04-24 at 12:21 -0400, Allison wrote:
Another equally sneeky/sleezy trick was to force NOPs
(00h) on the buss
till you hit the rom address where you disable the force nop logic.
That's slow (takes 61.4mS at 4mhz) though.
Only to a computer... That is .0614 seconds, considerably less than
a tenth of a second. Studies have shown that most people cannot even
detect intervals of less than a tenth of a second. Methinks thou dost
protest too much...
Peace,
Warren E. Wolfe
wizard at voyager.net
11:20 p.m.
New subject: Time perception [was Re: Hand-rolling a CP/M machine]
Studies have shown that most people cannot even detect
intervals of
less than a tenth of a second.
Under some circumstances, perhaps. Delay from flipping a switch to a
light going on, for example.
But if, for example, the interval in question is the time between two
sharp clicks of sound (the specific case I'm thinking of is pool balls
colliding), I feel quite sure most people could get well below a tenth
of a second. If it's the time difference between two adjacent lights
going on, perhaps even shorter - I suspect detecting the sign of the
difference is be easier than detecting its relative magnitude, though I
haven't tried it, not even on just myself.
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