> -----Original Message----- > From: space...@gmail.com > Sent: Sun, 19 Jul 2015 21:14:45 -0600 > To: cctalk@classiccmp.org > Subject: Re: Multibus arbiter design > > On Sun, Jul 19, 2015 at 4:01 PM, N0body H0me <n0body.h...@inbox.com> > wrote: >> A quick search on the "Site Which Must Not Be Named" shows >> some NOS 8289's for about $7 each, including postage. I dunno, >> just sayin-- why re-invent the wheel? > > 1. The 8289, being bipolar, draws an absurd amount of current on +5V. > Well over 100mA IIRC. If I were going that route, I'd want to use the > 82C89, which is even harder to find and more expensive. > > 2. The 8289 is specifically designed for the 8086 maximum-mode bus > interface, which is essentially unlike any other microprocessor's bus > interface, so it will take nearly as much extra logic to convert the > signals to what's needed for the 8289 as it would to just implement a > suitable bus arbiter. > > 3. $7 is a lot to pay for something that I can implement in the FPGA > for no incremental cost. > > 4. If I want to build more cards in five years, how much with a NOS > 8289 cost then? > > 5. If I'm going to sell the card, which there's some chance of > happening (admittedly small), I don't want to depend on availability > and price of NOS parts. > > If there was any particular magic involved in implementing a Multibus > arbiter, I'd shy away from doing it. However, it appears to actually > be rather simple. The reason for my request for examples was so that I > could study a few known working designs and make sure that there isn't > some trick to it that I've overlooked.
I just happened to see the parts you mentioned on EPay, so I posted that. Apparently, the 8289 is something of a square wheel (at least, for your application, anyway) and not a good fit. Anyways, just trying to be helpful. That's why I'm...... --n0body ____________________________________________________________ FREE ONLINE PHOTOSHARING - Share your photos online with your friends and family! Visit http://www.inbox.com/photosharing to find out more!
