The Apple II and Macintosh GCR (6-and-2 encoding) use 4us, 8us and 12us intervals.
The old Apple II GCR (5-and-3) doesn't use the 12us interval, but this format is far to be the most common.
The Apple II and Macintosh GCR (6-and-2 encoding) use 4us, 8us and 12us intervals.
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6-and-2 encoding table hide
6-bit value GCR code[27][24][26][25][22]
hex bin bin hex
0x00 00.0000 1001.0110 0x96
0x01 00.0001 1001.0111 0x97
0x02 00.0010 1001.1010 0x9A
0x03 00.0011 1001.1011 0x9B
0x04 00.0100 1001.1101 0x9D
0x05 00.0101 1001.1110 0x9E
0x06 00.0110 1001.1111 0x9F
0x07 00.0111 1010.0110 0xA6
0x08 00.1000 1010.0111 0xA7
0x09 00.1001 1010.1011 0xAB
0x0A 00.1010 1010.1100 0xAC
0x0B 00.1011 1010.1101 0xAD
0x0C 00.1100 1010.1110 0xAE
0x0D 00.1101 1010.1111 0xAF
0x0E 00.1110 1011.0010 0xB2
0x0F 00.1111 1011.0011 0xB3
6-bit value GCR code[27][24][26][25][22]
hex bin bin hex
0x10 01.0000 1011.0100 0xB4
0x11 01.0001 1011.0101 0xB5
0x12 01.0010 1011.0110 0xB6
0x13 01.0011 1011.0111 0xB7
0x14 01.0100 1011.1001 0xB9
0x15 01.0101 1011.1010 0xBA
0x16 01.0110 1011.1011 0xBB
0x17 01.0111 1011.1100 0xBC
0x18 01.1000 1011.1101 0xBD
0x19 01.1001 1011.1110 0xBE
0x1A 01.1010 1011.1111 0xBF
0x1B 01.1011 1100.1011 0xCB
0x1C 01.1100 1100.1101 0xCD
0x1D 01.1101 1100.1110 0xCE
0x1E 01.1110 1100.1111 0xCF
0x1F 01.1111 1101.0011 0xD3
6-bit value GCR code[27][24][26][25][22]
hex bin bin hex
0x20 10.0000 1101.0110 0xD6
0x21 10.0001 1101.0111 0xD7
0x22 10.0010 1101.1001 0xD9
0x23 10.0011 1101.1010 0xDA
0x24 10.0100 1101.1011 0xDB
0x25 10.0101 1101.1100 0xDC
0x26 10.0110 1101.1101 0xDD
0x27 10.0111 1101.1110 0xDE
0x28 10.1000 1101.1111 0xDF
0x29 10.1001 1110.0101 0xE5
0x2A 10.1010 1110.0110 0xE6
0x2B 10.1011 1110.0111 0xE7
0x2C 10.1100 1110.1001 0xE9
0x2D 10.1101 1110.1010 0xEA
0x2E 10.1110 1110.1011 0xEB
0x2F 10.1111 1110.1100 0xEC
6-bit value GCR code[27][24][26][25][22]
hex bin bin hex
0x30 11.0000 1110.1101 0xED
0x31 11.0001 1110.1110 0xEE
0x32 11.0010 1110.1111 0xEF
0x33 11.0011 1111.0010 0xF2
0x34 11.0100 1111.0011 0xF3
0x35 11.0101 1111.0100 0xF4
0x36 11.0110 1111.0101 0xF5
0x37 11.0111 1111.0110 0xF6
0x38 11.1000 1111.0111 0xF7
0x39 11.1001 1111.1001 0xF9
0x3A 11.1010 1111.1010 0xFA
0x3B 11.1011 1111.1011 0xFB
0x3C 11.1100 1111.1100 0xFC
0x3D 11.1101 1111.1101 0xFD
0x3E 11.1110 1111.1110 0xFE
0x3F 11.1111 1111.1111 0xFF
The three horizontals lines are the timings intervals coming out from the drive. You will get the same thing from an oscilloscope if you read an GCR 6 and 2 disk.george wrote: ↑Wed Jun 03, 2020 1:20 amIf you are right there must be a logical explanation to it. Can you provide it especially when Apple2's GCR does not allow more than 3 consecutive zeros? I am not familiar with your software at all and the screenshot is not comprehensible. Moreover it does not come form a logic analyzer or a scope...
More reading needed maybe ? :
The bit time is nominally approximately 4 microseconds.
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interval between pulses
fast wr slow wr
data nominal slow rd fast rd
----- ------- ------- -------
11 4 us 4.7 us 3.4 us
101 8 us 9.4 us 6.8 us
1001 12 us 14.1 us 10.2 us
10001 16 us 18.8 us 13.6 us
The A2R support is planed in the hxc software. should be there quite soon.george wrote: ↑Thu Jun 04, 2020 2:16 pmOK, thank you, I must have understood the 12μs measurement (it encompasses the leading 1 bit). The DISK II drive amp based on MC3470 also generates random data due to AGC when no data is read from the RW head.
What is the time resolution of the HxC? Do you think it could handle the a2r 125nS disk image format in order to "play" it? https://applesaucefdc.com/a2r/
This would be a giant step into the Apple2 world. Even the author of a2r is lacking abilities to build a "player" for his own format. It would be interesting to discover what percentage of all those already made a2r images would be accurate enough to run the imaged software.
on what exactly ?
This is in the beta version since some months.