mirror of
https://github.com/iKarith/beneath-apple-dos.git
synced 2024-10-12 00:23:45 +00:00
133 lines
2.8 KiB
Plaintext
133 lines
2.8 KiB
Plaintext
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.na
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.fi
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.ll60
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.br
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SECOND PRINTING CORRECTIONS
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.sp3
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3-3
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.sp1
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Data bits are recorded on the
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diskette in precise intervals. For
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the purposes of this discussion, the
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demarcation of these intervals will
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be depicted by a clock bit. Using
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this representation, data written to
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and read back from the diskette takes
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the form shown in Figure 3.2. The
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data pattern shown represents a
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binary value of 101.
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.sp3
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3-10
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.sp1
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at least as long as a typical Gap 3
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(in practice its length is usually
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more than 400 sync bytes, enabling it
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to serve as a Gap 3 type for Address
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Field number 0 (See Figure 3.7 for
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clarity).
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.sp3
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3-17
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.sp1
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page.*
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.sp1
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diagrammed in Figure 3.21.*
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.sp1
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*Figures 3.20 and 3.21 present the
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nibblizing process used by the "6 and
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2" encoding technique. However, the
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concept is the same for the "5 and 3"
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technique.
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.sp3
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4-17
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.sp1
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.nf
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occurred. Either a bad checksum was detected on the data in a
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.fi
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.sp1
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program given there will read any
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track/sector on an unprotected
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diskette into memory, allowing the
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user to examine it or modify the data
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and then, optionally, rewrite it to a
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diskette. Using such a program is
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very important when learning about
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diskette formats and when fixing
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clobbered data.
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.sp3
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5-2
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.sp1
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The file manager, occupying about
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2.8K, is a collection of
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.bp
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5-5 (note correction to correction - first $3F2 is ok)
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.sp1
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.nf
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change $3F2 to handle your own RESETs, EOR (exclusive
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OR) the new value at $3F3 with a $A5 and store the
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result in the power-up byte.
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.sp3
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.fi
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6-5
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.sp1
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NOTE: RWTS uses zero-page location
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$48, which is also used by the
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APPLE
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monitor to hold the P-register value.
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Location $48 should be set to zero
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after each call to RWTS.
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.sp3
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6-11
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.sp1
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.nf
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04/05 - Byte offset of current file position*
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.sp1
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.fi
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*The current file position is updated
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to point to the byte following the
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data read or written.
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.sp3
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8-5
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.sp1
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.nf
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9E51-9E7F An image of the DOS page 3 jump vector which the
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above routine copies to $3D0-$3FF. See Chapter 5 for
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a description of its contents.
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.sp3
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8-36
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.sp1
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B9A0-B9FF SEEKABS routine.
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Move disk arm to desired track.
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Calls arm move delay subroutine ($BA00).
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.sp3
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8-37
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.sp1
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BA00-BA10 Arm move delay subroutine.
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.sp3
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A-3
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.sp1
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.fi
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A diskette containing these five
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programs is available at a reasonable
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cost directly from Quality Software,
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6660 Reseda Blvd., Reseda, CA. or
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telephone (213) 344-6599.
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.bp
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A-12
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.sp1
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at location $03 (the volume number
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should match the volume number of the
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other tracks), and then begin
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execution at $800. INIT will return
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to the monitor upon completion. If
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the track can not be formatted for
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some reason (eg. physical damage or
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problems with the disk drive itself)
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a return code is printed. For
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example:
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.sp3
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A-20
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.sp1
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.nf
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800G (Run the COPY program)
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.br
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