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From: mlelstv@immd4.informatik.uni-erlangen.de (Michael van Elst )
Newsgroups: comp.sys.amiga
Subject: Re: Are there any programs that allow reading Apple ][ disks?
Keywords: disk encoding, MFM, GCR, 13-sector, 16-sector, ProDOS, 5.25, 3.5
Message-ID: <491@medusa.informatik.uni-erlangen.de>
Date: 18 Aug 89 14:12:53 GMT
References: <495@tardis.Tymnet.COM> <15704@pollux.UUCP> <12938@grebyn.com>
Organization: IMMD IV, University of Erlangen, W-Germany
Lines: 23

ckp@grebyn.com (Checkpoint Technologies) writes:

>In article <15704@pollux.UUCP> bjc@pollux.UUCP () writes:
>>
>>The RKM states that the GCR capability in the Amiga is the Apple version.
>>
>As far as I know, the Amiga does not have a GCR translation table built
>in. It does have the ability to read CGR disks (witness: Disk-2-Disk and
>Mac-2-Dos and AMAX), but this is because the Amiga's disk controller
>gives the CPU data below the formatter level, so the CPU can perform
>whatever encoding it desired.

There is a limited hardware feature for GCR decoding. It allows
less CPU overhead when reading Apple-II style GCR code..

The Apple-II uses a simple shift register that samples raw data
(just like the Amiga hardware) and transfers it's contents into
a latch everytime the MSB (bit 7) is equal 1, then the shifter is
cleared. A similar mode can be used with the Amiga hardware.

				Michael van Elst

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