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There are 15 commands which the FDC uPD765a wil execute.Each of these commands require multiple 8-bytes to fully specify the operation which the processor wishes the FDC to perform. 
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The following commands are available :
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00 - INVALID
01 - INVALID
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02 - FDC_COMMAND_READ_A_TRACK
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF  0  0  0  0  1  0
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data transfer between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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03 - FDC_COMMAND_SPECIFY
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0  0  0  0  0  0  1  1
        W <---SRT---> <---HUT--->
        W <-------HLT--------> ND
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04 - FDC_COMMAND_SENSE_DRIVE_STATUS
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0  0  0  0  0  1  0  0
        W  0  0  0  0  0  HDSDS1DS0
Result  R ----------ST3----------	Status information about FDD
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05 - FDC_COMMAND_WRITE_DATA
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  0  0  1  0  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    W ----------------------- Data transfer between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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06 - FDC_COMMAND_READ_DATA
---------------------------
          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  0  0  1  1  0
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data transfer between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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07 - FDC_COMMAND_RECALIBRATE
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0  0  0  0  0  1  1  1
        W  0  0  0  0  0  0DS1DS2
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08 - FDC_COMMAND_SENSE_INTERRUPT_STATUS
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0  0  0  0  1  0  0  0
Result  R  ---------ST0----------	Status information about the FDC at the end of each seek operation
        R  ---------PCN----------	PCN = Present Cylinder No.
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09 - FDC_COMMAND_WRITE_DELETED_DATA
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  0  1  0  0  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    W ----------------------- Data transfer between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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0A - FDC_COMMAND_READ_ID
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0 MF  0  0  1  0  1  0
        W  0  0  0  0  0HDSDS1DS2
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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0B - INVALID
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0C - FDC_COMMAND_READ_DELETED_DATA
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  0  1  1  0  0
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data transfer between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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0D - FDC_COMMAND_FORMAT_A_TRACK
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0 MF  0  0  1  1  0  0
        W  0  0  0  0  0HDSDS1DS2
        W ----------N------------ 	Bytes/Sector
        W ---------SC------------	Sectors/Track
        W ---------GPL-----------	Gap 3
        W ----------D------------	Filler byte
Exec      -----------------------	FDC Formats an entire track
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	In this case, the sector ID information has no meaning
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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0E - INVALID
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0F - FDC_COMMAND_SEEK
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W  0  0  0  0  1  1  1  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------NCN----------	New Cylinder Number
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10 - INVALID
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11 - FDC_COMMAND_SCAN_EQUAL
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  1  0  0  0  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data compared between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
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12 - INVALID
13 - INVALID
14 - INVALID
15 - INVALID
16 - INVALID
17 - INVALID
18 - INVALID
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19 - FDC_COMMAND_SCAN_LOW_OR_EQUAL
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  1  0  0  0  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data compared between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
---------------------------
1A - INVALID
1B - INVALID
1C - INVALID
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1D - FDC_COMMAND_SCAN_HIGH_OR_EQUAL
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          D7 D6 D5 D4 D3 D2 D1 D0
Command W MT MF SK  1  0  0  0  1
        W  0  0  0  0  0HDSDS1DS2
        W ----------C------------	Sector ID Information
        W ----------H------------
        W ----------R------------
        W ----------N------------
        W ---------EOT-----------
        W ---------GPL-----------
        W ---------DTL-----------
Exec    R -----------------------	Data compared between the FDD and main system
Result  R ----------ST0----------	Status information after command execution
        R ----------ST1----------
        R ----------ST2----------
        R -----------C-----------	Sector ID information after command execution
        R -----------H-----------
        R -----------R-----------
        R -----------N-----------
---------------------------
1E - INVALID
1F - INVALID
; ---------------------------
MT	Multitrack - If MT is high, a Multitrack operation is performaed. If MT = 1, after finishing Read/Write operation on side 0, FDC will automatically start searching for sector 1 on side 1.
MF	FM or MFM Mode - If MF is low, FM mode is selected, and if it is high, MFM mode is selected.
SK	Skip - SK stands for Skip Deleted Data Address mark.
; ---------------------------
; Drive and Head Select Values
; ---------------------------
; HDS - Head Select - Head 1 selected when "1" (high). Head 0 selected when "0" (low).
; DS1DS0 - Drive Select - Selects FDD unit number 00,01,02 or 03
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Sector ID Information prior to command execution
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C 	Cylinder Number C stands for the current selected Cylinder track number 0 through 76 of the medium
H 	Head Address 	H stands for head number 0 or 1, as specified in the ID field
R 	Record 			R stands for the Sector Number which will be read or written.
N 	Number 			N stands for the number of data bytes written in a sector 
EOT End Of Track 	EOT stands for the final Sector number of a Cylinder
GPL Gap Length 		GPL stands for the length of Gap 3 (spacing between sectors excluding VCO Sync field)
DTL Data Length 	When N is defined as 00, DTL stands for the data length which users are going to read out or write into the sector.
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Example :
a) read a sector &c1 at track 0 with MFM Data
46-00 00 00 c1 02 c1 2a ff
Note : last parameter DTL can be anything as N=2

b) read a deleted 2 sectors &45 and &46 at track 2 with MFM Data
4c-00 00 00 45 02 46 2a ff
Note : last parameter DTL can be anything as N=2

c) scan or equal sector &c1 at track 10 with MFM Data
41-00 00 0a c1 02 c1 2a ff
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