beneath-apple-dos/CHANGES-2nd-printing.txt
2017-07-21 07:59:50 -07:00

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.na
.fi
.ll60
.br
SECOND PRINTING CORRECTIONS
.sp3
3-3
.sp1
Data bits are recorded on the
diskette in precise intervals. For
the purposes of this discussion, the
demarcation of these intervals will
be depicted by a clock bit. Using
this representation, data written to
and read back from the diskette takes
the form shown in Figure 3.2. The
data pattern shown represents a
binary value of 101.
.sp3
3-10
.sp1
at least as long as a typical Gap 3
(in practice its length is usually
more than 400 sync bytes, enabling it
to serve as a Gap 3 type for Address
Field number 0 (See Figure 3.7 for
clarity).
.sp3
3-17
.sp1
page.*
.sp1
diagrammed in Figure 3.21.*
.sp1
*Figures 3.20 and 3.21 present the
nibblizing process used by the "6 and
2" encoding technique. However, the
concept is the same for the "5 and 3"
technique.
.sp3
4-17
.sp1
.nf
occurred. Either a bad checksum was detected on the data in a
.fi
.sp1
program given there will read any
track/sector on an unprotected
diskette into memory, allowing the
user to examine it or modify the data
and then, optionally, rewrite it to a
diskette. Using such a program is
very important when learning about
diskette formats and when fixing
clobbered data.
.sp3
5-2
.sp1
The file manager, occupying about
2.8K, is a collection of
.bp
5-5 (note correction to correction - first $3F2 is ok)
.sp1
.nf
change $3F2 to handle your own RESETs, EOR (exclusive
OR) the new value at $3F3 with a $A5 and store the
result in the power-up byte.
.sp3
.fi
6-5
.sp1
NOTE: RWTS uses zero-page location
$48, which is also used by the
APPLE
monitor to hold the P-register value.
Location $48 should be set to zero
after each call to RWTS.
.sp3
6-11
.sp1
.nf
04/05 - Byte offset of current file position*
.sp1
.fi
*The current file position is updated
to point to the byte following the
data read or written.
.sp3
8-5
.sp1
.nf
9E51-9E7F An image of the DOS page 3 jump vector which the
above routine copies to $3D0-$3FF. See Chapter 5 for
a description of its contents.
.sp3
8-36
.sp1
B9A0-B9FF SEEKABS routine.
Move disk arm to desired track.
Calls arm move delay subroutine ($BA00).
.sp3
8-37
.sp1
BA00-BA10 Arm move delay subroutine.
.sp3
A-3
.sp1
.fi
A diskette containing these five
programs is available at a reasonable
cost directly from Quality Software,
6660 Reseda Blvd., Reseda, CA. or
telephone (213) 344-6599.
.bp
A-12
.sp1
at location $03 (the volume number
should match the volume number of the
other tracks), and then begin
execution at $800. INIT will return
to the monitor upon completion. If
the track can not be formatted for
some reason (eg. physical damage or
problems with the disk drive itself)
a return code is printed. For
example:
.sp3
A-20
.sp1
.nf
800G (Run the COPY program)
.br