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PC8477BVF-1 Datasheet(PDF) 24 Page - National Semiconductor (TI) |
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PC8477BVF-1 Datasheet(HTML) 24 Page - National Semiconductor (TI) |
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24 / 54 page  40 Command Set Description (Continued) TABLE 4-4 Effect of Drive Mode and Data Rate on Format and Write Commands Drive GAP2 Length Portion of GAP2 Data Rate Mode Written During Re-Written by Write Format Data Command 250300500 kbs Conventional 22 bytes 0 bytes Perpendicular 22 bytes 19 bytes 1 Mbs Conventional 22 bytes 0 bytes Perpendicular 41 bytes 38 bytes TABLE 4-4A Effect of GAP and WG on Format and Write Commands Mode GAP2 Length Portion of GAP2 GAP WG Description Written During Re-Written by Write Format Data Command 0 0 Conventional 22 bytes 0 bytes 0 1 Perpendicular 22 bytes 19 bytes (s500 kbs) 1 0 Reserved 22 bytes 0 bytes (Conventional) 1 1 Perpendicular 41 bytes 38 bytes (1 Mbs) Perpendicular Recording type disk drives have a Pre-Erase Head which leads the ReadWrite Head by 200 mm which translates to 38 bytes at the 1 Mbs data transfer rate (19 bytes at 500 kbs) The increased spacing between the two heads requires a larger GAP2 between the Address Field and Data Field of a sector at 1 Mbs (See Perpendicular Format in Table 4-1) This GAP2 length of 41 bytes (at 1 Mbs) will ensure that the Preamble in the Data Field is completely ‘‘pre-erased’’ by the Pre-Erase Head Also dur- ing Write Data operations to a perpendicular drive a portion of GAP2 must be rewritten by the controller to guarantee that the Data Field Preamble has been pre-erased (see Ta- ble 4-4) 429 Read Data Command The Read Data command reads logical sectors containing a Normal Data AM from the selected drive and makes the data available to the host mP After the last Command Phase byte is written the controller will simulate the Motor On Time for the selected drive internally The user must turn on the drive motor directly by enabling the appropriate drive and motor select disk interface outputs with the Digital Out- put Register (DOR) If Implied Seeks are enabled the controller will perform a Seek operation to the track number specified in the Com- mand Phase The controller will also issue a Sense Interrupt for the seek and wait the Head Settle time specified in the Mode command The correct ID information (track head sector bytes per sector) for the desired sector must be specified in the com- mand bytes See Table 4-5 Sector Size Selection for details on the bytes per sector code In addition the End of Track Sector Number (EOT) should be specified allowing the con- troller to read multiple sectors The Data Length byte is a don’t care and should be set to FF (hex) TABLE 4-5 Sector Size Selection Bytes per Number of Bytes Sector Code in Data Field 0 128 1 256 2 512 3 1024 4 2048 5 4096 6 8192 7 16384 The controller then starts the Data Separator and waits for the Data Separator to find the next sector Address Field The controller compares the Address Field ID information (track head sector bytes per sector) with the desired ID specified in the Command Phase If the sector ID bytes do not match then the controller waits for the Data Separator to find the next sector Address Field The ID comparison process repeats until the Data Separator finds a sector Ad- dress Field ID that matches that in the command bytes or until an error occurs Possible errors are 1 The mP aborted the command by writing to the FIFO If there is no disk in the drive the controller will hang up The mP must then take the controller out of this hung state by writing a byte to the FIFO This will put the con- troller into the Result Phase 2 Two index pulses were detected since the search began and no valid ID has been found If the track address ID differs the WT bit or BT bit (if the track address is FF hex) will be set in ST2 If the head sector or bytes per sector code did not match the ND bit is set in ST1 If the Ad- dress Field AM was never found the MA bit is set in ST1 3 The Address Field was found with a CRC error The CE bit is set in ST1 24 |
Similar Part No. - PC8477BVF-1 |
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Similar Description - PC8477BVF-1 |
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