Envelope-to: craig@sbc-85.com
Delivery-date: Thu, 25 Apr 2024 19:41:19 -0500
Date: Fri, 26 Apr 2024 00:41:03 +0000
To: craig@sbc-85.com
From: Herbert Johnson <hjohnson@retrotechnology.com>
Subject: Re: pro-log floppy disk controller STD bus - manuals
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Issues of single or double density on 8-inch controllers, is=20
historically about the speed of the microprocessor. A slow clocked Z80=20
or especially 8080, can't keep up with double-density 8" data speeds. A=20
DMA controller changes that, it provides the necessary data-transfer=20
speed. Data speeds on 5.25-inch drives are half speeds of 8-inch drives.=20
On 3.5" drives, they are more like 8-inch drives, but early models did=20
not support 1.4M capacity (amounting to double density 8-inch rates).

ON the question of -12 volts. My guess is, some analog PPL electronics?

Those are my immediate remarks to your notes. - regards Herb

On 4/25/2024 6:49 PM, craig@sbc-85.com wrote:
> Hi Herb,
>=20
> Thanks again for the cut sheets.
>=20
> Doing a quick comparison, I wonder if the major selling point of the 8510=
 was that it uses a phase locked loop for the data separator?  I imagine th=
e PLL is that business in the upper left portion of the card nearest the ej=
ector. Maybe other advantages will be more evident when I read the 8510 man=
ual, but just from the sell sheets they really aren't making their case for=
 the (presumably) much more expensive 8510..
> Both are based on the 765 controller, I cant see if they are both using t=
he 765C
> DMA and interrupt specifications seem to be the same
> Both can handle up to four drives
> The 8500 only needs +5V, the 8510 needs 5V and -12V.  the 765 is 5V only =
so I wonder what is using the -12 on the 8510?
> The 8500 can do 3-1/2 & 5-1/4 & 8" disks but the 8" is only single densit=
y.  The 8510 has two hardware versions, the 8510 does 8" and the 8510-2 doe=
s 5&3".
> But.... by themselves either the 8500 or 8510 can only do single density =
on 8" drives.  The 8510 can do double density 8" but 'most often' it requir=
es a DMA controller.
> Standard drive pinout, for each drive size, the 8500 and 8510 uses the sa=
me cable, e.g., both use CA0005-2 for dual 5-1/4" drives
>=20
> Anyway, as I mentioned in my last email the similarity justifies getting =
the user's manual for the 8510.
>=20
> Regards
> craig
Herb Johnson, New Jersey USA
http://www.retrotechnology.com or .net
preserve and restore 1970's personal computing
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