19 Jul
2015
19 Jul
'15
1:50 a.m.
Is anyone aware of any published detailed designs of Multibus
arbitration circuitry, NOT using the Intel bus arbiter chips (e.g.,
8218, 8219, 8289, 82289)? I know various vendors making Multibus CPU
cards for non-Intel CPUs (e.g., 68K or NS 32K) sometimes designed
their own arbiters out of TTL and/or PALs, but I haven't found any
schematics. The only thing I've found so far is an application note "A
Multibus Arbiter Design for 10 MHz Processors" in the 1988 AMD PAL
Device Handbook, but I'd like to see other examples.
I'm considering designing a Multibus I/O card that needs to be a bus
master, and while an 8289 or 82C89 would do what I want, they're
relatively hard to find and expensive, so I'd rather just do it in my
FPGA, with suitable buffering to meet the Multibus electrical specs.
It appears that the inner workings of the Intel 8289 arbiter are
documented in US patent 4,257,095.
The Intel MDS-800 circa 1975 used a bunch of TTL, but it was pretty
tightly intertwined with 8080-specific logic, and since the MDS-800
predated the Multibus spec and has a few obvious differences from it,
I don't think it serves as a particularly good bus arbiter design
example.
6:01 p.m.
-----Original Message-----
From: spacewar at gmail.com
Sent: Sun, 19 Jul 2015 13:15:37 -0600
To: cctalk at classiccmp.org
Subject: Re: Multibus arbiter design
On Sun, Jul 19, 2015 at 9:21 AM, Al Kossow <aek at bitsavers.org> 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?
--n0body
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SUN I or II board?
Cool, the Sun 2 CPU board doc has description and schematic.
11:14 p.m.
On Sun, Jul 19, 2015 at 4:01 PM, N0body H0me <n0body.h0me at 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.
20 Jul
20 Jul
2:04 a.m.
-----Original Message-----
From: spacewar at gmail.com
Sent: Sun, 19 Jul 2015 21:14:45 -0600
To: cctalk at classiccmp.org
Subject: Re: Multibus arbiter design
On Sun, Jul 19, 2015 at 4:01 PM, N0body H0me <n0body.h0me at inbox.com>
wrote:
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
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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.
3285
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3286
days old
6 comments
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