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FDC37C78-HT Datasheet(PDF) 29 Page - Microchip Technology |
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FDC37C78-HT Datasheet(HTML) 29 Page - Microchip Technology |
29 / 82 page ![]() 29 COMMAND SET/DESCRIPTIONS Commands can be written whenever the FDC is in the command phase. Each command has a unique set of needed parameters and status results. The FDC checks to see that the first byte is a valid command and, if valid, proceeds with the command. If it is invalid, an interrupt is issued. The user sends a Sense Interrupt Status command which returns an invalid command error. Refer to Table 18 or explanations of the various symbols used. Table 19 lists the required parameters and the results associated with each command that the FDC is capable of performing. Table 18 - Description of Command Symbols SYMBOL NAME DESCRIPTION C Cylinder Address The currently selected address; 0 to 255. D Data Pattern The pattern to be written in each sector data field during formatting. D0, D1, D2, D3 Drive Select 0-3 Designates which drives are perpendicular drives on the Perpendicular Mode Command. A "1" indicates a perpendicular drive. DIR Direction Control If this bit is 0, then the head will step out from the spindle during a relative seek. If set to a 1, the head will step in toward the spindle. DS0, DS1 Disk Drive Select DS1 DS0 DRIVE 0 0 drive 0 0 1 drive 1 1 0 drive 2 1 1 drive 3 DTL Special Sector Size By setting N to zero (00), DTL may be used to control the number of bytes transferred in disk read/write commands. The sector size (N = 0) is set to 128. If the actual sector (on the diskette) is larger than DTL, the remainder of the actual sector is read but is not passed to the host during read commands; during write commands, the remainder of the actual sector is written with all zero bytes. The CRC check code is calculated with the actual sector. When N is not zero, DTL has no meaning and should be set to FF HEX. EC Enable Count When this bit is "1" the "DTL" parameter of the Verify command becomes SC (number of sectors per track). EFIFO Enable FIFO This active low bit when a 0, enables the FIFO. A "1" disables the FIFO (default). EIS Enable Implied Seek When set, a seek operation will be performed before executing any read or write command that requires the C parameter in the command phase. A "0" disables the implied seek. EOT End of Track The final sector number of the current track. GAP Alters Gap 2 length when using Perpendicular Mode. GPL Gap Length The Gap 3 size. (Gap 3 is the space between sectors excluding the VCO synchronization field). H/HDS Head Address Selected head: 0 or 1 (disk side 0 or 1) as encoded in the sector ID |
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