Re: Asteroids Deluxe hacking unsuccessful so far

Its of interest to me, keep the discussion here on the list.

David
----- Original Message -----
From: <solarfox@texas.net>
To: <vectorlist@synthcom.com>
Sent: Wednesday, April 25, 2001 6:06 AM
Subject: Re: VECTOR: Asteroids Deluxe hacking unsuccessful so far

> On Tue, 24 Apr 2001 23:52:14 -0700 (PDT), you wrote:
>
> >* I have implemented Gary's 7400 array of gates for the !CE signal to the
> >EPROM
>
> Er... this might be your problem, then. That gate array (Joe's two-NOR
> arrangement would work as well, BTW) generates a HIGH only when A=0 and
> B=1, but I don't think that's what you really want. Remember that CE* is
> an active-LOW signal, so regardless of which way you wired the inputs:
>
> A=A15 B=WR* O=CE* A=WR* B=A15 O=CE*
> --------------------- ---------------------
> 0 0 0 0 0 0
> 0 1 1 0 1 1
> 1 0 0 1 0 0
> 1 1 0 1 1 0
>
> ...you've got a situation where the EPROM's chip-select signal is LOW
> at times you probably don't want it to be. (The same would apply if
you're
> running the RD* signal to the gates instead of WR*, by the way.) To
> chip-select the EPROM, I think you're going to need something more
complex,
> since you not only want the EPROM to be selected when both A15 and RD* are
> low, but you have to stay out of the way of any RAM or memory-mapped I/O
> devices in the memory map.
>
> Let me go get some coffee and dig up an ASTEROIDS DELUXE schematic, and
> get back to you. :) (BTW - Neil, feel free to contact me directly so we
> don't continue to flood the list with pages of ASCII art, unless the list
> finds the discussion of interest...?)
>
> --------------------------------------------------------------------------

---
> "There is no virtue in suffering fools gladly, for it only encourages them
to
> persist in their foolishness."                                --Kehlog
Albran
> --------------------------------------------------------------------------
---
> solarfox@DON'TMESSWITHtexas.net                              (Gary Akins
jr.)
> http://lonestar.texas.net/~solarfox
> --------------------------------------------------------------------------
---
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