'Parallel Slave Port (was: Instruction encodings)'
| Well, I won't take this personally since I hired into Microchip after
the slave port was defined. The guy who designed it is an Intel-Ex
and was very familiar with the 804X. The port is primarily
constrained by the pin availability. There wasn't a good place to put
an address pin.
BTW, we do customer surveys frequently when defining a new device. If
some of you would like to participate, respond to me directly and
include your address, as we visit the country/world by region.
______________________________ Reply Separator _________________________________
Subject: Re: Re: Instruction encodings (was: Code error)
Author: Eric Smith <BROUHAHA.COM> at Internet_Exchange eric
Date: 2/25/97 5:01 PM
John Payson <MCS.NET> wrote: supercat
> IMHO, the host port as Microchip implements it is still somewhat
> limitted, however, since there is no good way to distinguish commands from
> data without adding more external logic. Think what you like about the
> 8042's instruction set, but having two read addresses and two write addresses
> from the host's point of view can really improve things a lot.
Agreed. When I first saw the specs, I thought, "Wow, finally a decent
8041/8042 replacement" (since Intel's never done a decent one since).
Given how ubiquitous the 804x are, you'd think someone at Microchip would
have bothered to actually look at it for ideas as to how to make a *usable*
host port. :-( Mitsubishi, who I usually don't credit for being
exceptionally clueful, managed to get that right on their 3745x parts.
I'd really like to see three separate registers for data and commands written
by the host to the PIC, but even a single register for both would be OK if
they'd save a 9th bit like to 804x.
Sigh. Maybe someday some semi company will accidentally stumble onto the
combination of great engineering *and* low prices. I haven't yet become
convinced that it's impossible.
Maybe we could convince Microchip to send a few of us very early
(pre-tapeout) engineering specs to look over to try to avoid silly design
flaws and limitations like this.
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