Alt-BEAM Archive
Message #02248
To: "'Wouter Brok'" w.j.m.brok@stud.tue.nl
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Mon, 12 Apr 1999 12:49:43 -0700
Subject: [alt-beam] Re: Linked BiCores; How Does The Slave Cycle?
content-type: text/plain
Very sharp Wouter!
Actually I send those waveforms to you privately but as long as we are
discussing them here I have attached them to this reply.You will find one
additional circuit which exploits the overvoltage at the input of the
"isolated" suspended BiCore to generate some additional supply voltages
(+7.5V and -2.5V).
The graphs are approximations I made with a CAD program. They don't have a
calibrated time axis. You are correct that the 74HC04 and 74HCU04 would have
the same exponential curve using the same RC parts but a different period
because of the difference in thresholds. The 74HC04 inverter has a voltage
gain of about 100 and a narrow (50mV) gap around 2.5V between the upper and
lower thresholds. The 74HCU04 inverter has a much smaller gain and widely
separated upper and lower thresholds. In this description, threshold means
the input voltage level at which the output voltage starts to change. The
graphs for the HC/AC240 are very similar to the 74HC/AC04 so the example
holds for both cases. However there are important effects related to output
load current and obviously the 74HC04 has much less current capability
(higher output impedance than the 74AC04 and 74HC/AC240. Power supply noise
and "ground bounce" can change the period of a master or slave BiCore by
50% which could be suppressed by good supply decoupling and supply bus
layout for more repeatable results. Of course, this all falls into the
category of "feedback" so you can explore ways to the modulate BiCore pulse
width in response to change in load by deliberately allowing a certain
amount of noise to influence the BiCore period. This is the way in which
BEAM design exploits electronic circuit behaviour on the edge of chaos
giving rise to such complex and surprising behaviour in BEAM bots.
<>
enjoy
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
> -----Original Message-----
> From: Wouter Brok [SMTP:w.j.m.brok@stud.tue.nl]
> Sent: Monday, April 12, 1999 12:07 AM
> To: beam@corp.sgi.com
> Subject: RE: Linked BiCores; How Does The Slave Cycle?
>
> Hello, again
>
> Actually, having a look at them I come up with a couple of questions:
> -In the circuit of the 'suspended' bicore you use the 74HC04 and the
> 74HCU04. I don't know what the difference is between them, but what
> suprises me is that the exponential parts in the graphs don't seem to be
> the same, while I assume the resistors and capacitors are. How is that?
> -Are the time-scales the same for all graphs?
>
> How do the graphs look for the 74HC240; I don't know how much time it
> costs
> to make them, but if it doesn't take much I would like to see them; or are
> they the same as any of those?
>
> Regards
>
> Wouter Brok
>
>
>
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