Post by thread: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. Rgds, Brian. ______________________________ Reply Separator _________________________________ Subject: Re: Re[2]: Instruction encodings (was: Code error) Author: Eric Smith <spam_OUTericTakeThisOuTBROUHAHA.COM> at Internet_Exchange Date: 2/25/97 5:01 PM John Payson <.....supercatKILLspam@spam@MCS.NET> wrote: > 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. Cheers, Eric