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PC8477BV-1 Datasheet(PDF) 27 Page - National Semiconductor (TI) |
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PC8477BV-1 Datasheet(HTML) 27 Page - National Semiconductor (TI) |
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27 / 54 page  40 Command Set Description (Continued) 4215 Scan Commands The Scan commands allow data read from the disk to be compared against data sent from the mP There are three Scan commands to choose from Scan Equal Disk Data e mP Data Scan Low or Equal Disk Data s mP Data Scan High or Equal Disk Data t mP Data Each sector is interpreted with the most significant bytes first If the Wildcard mode is enabled in the Mode command an FF (hex) from either the disk or the mP is used as a don’t care byte that will always match equal After each sector is read if the desired condition has not been met the next sector is read The next sector is defined as the current sector number plus the Sector Step Size specified The Scan command will continue until the scan condition has been met or the EOT has been reached or if TC is assert- ed Read errors on the disk will have the same error conditions as the Read Data command If the SK bit is set sectors with deleted data marks are ignored If all sectors read are skipped the command will terminate with D3 of ST2 set (Scan Equal Hit) The Result Phase of the command is shown in Table 4-10 TABLE 4-10 Scan Command Termination Values Command Status Conditions Register 2 D2 D3 Scan Equal 0 1 Disk e mP 1 0 Disk i mP Scan Low 0 1 Disk e mP or Equal 0 0 Disk k mP 1 0 Disk l mP Scan High 0 1 Disk e mP or Equal 0 0 Disk k mP 1 0 Disk l mP 4216 Seek Command The Seek command issues step pulses to move the select- ed drive head in or out until the desired track number is reached During the Execution Phase of the Seek com- mand the track number to seek to is compared with the present track number The controller will determine how many step pulses to issue and the DIR disk interface output will indicate which direction the RW head should move The DRx BUSY bit is set in the MSR for the appropriate drive The controller will wait the Motor On time before issu- ing the first step pulse After the Motor On time the controller will enter the Idle Phase The execution of the actual step pulses occurs in the Drive Polling phase of the controller The step pulse rate is determined by the value programmed in the Specify com- mand An interrupt will be generated one step pulse period after the last step pulse is issued There is no Result Phase A Sense Interrupt command should be issued to determine the cause of the interrupt While the internal microengine is capable of multiple seeks on 2 or more drives at the same time software should en- sure that only one drive is seeking or recalibrating at a time This is because the drives are actually selected via the DOR which can only select one drive at a time No other command except a Sense Interrupt command should be is- sued while a Seek command is in progress If the extended track range mode is enabled with the ETR bit in the Mode command a fourth command byte should be written in the Command Phase to indicate the four most significant bits of the desired track number Otherwise only three command bytes should be written 4217 Sense Drive Status Command The Sense Drive Status command returns the status of the selected disk drive in ST3 This command does not gener- ate an interrupt 4218 Sense Interrupt Command The Sense Interrupt command is used to determine the cause of interrupt when the interrupt is a result of the change in status of any disk drive Four possible causes of the interrupt are 1 Upon entering the Result Phase of a Read Data command b Read Deleted Data command c Read a Track command d Read ID command e Write Data command f Write Deleted Data command g Format command h Scan command i Verify command 2 During data transfers in the Execution Phase while in the Non-DMA mode 3 Ready Changed State during the polling mode for an in- ternally selected drive (Occurs only after a hardware or software reset) 4 Seek Relative Seek or Recalibrate termination An interrupt due to reasons 1 and 2 does not require the Sense Interrupt command and is cleared automatically This interrupt occurs during normal command operations and is easily discernible by the mP via the MSR This interrupt is cleared reading or writing information fromto the Data Reg- ister (FIFO) Interrupts caused by reason 3 and 4 are identified with the aid of the Sense Interrupt command The interrupt is cleared after the first result byte has been read Use bits 5 6 and 7 of ST0 to identify the cause of the interrupt as shown in Table 4-11 TABLE 4-11 Status Register 0 Termination Codes Status Register 0 Cause Interrupt Seek Code End D7 D6 D5 1 1 0 Internal Ready Went True 0 0 1 Normal Seek Termination 0 1 1 Abnormal Seek Termination Issuing a Sense Interrupt command without an interrupt pending is treated as an Invalid command If the extended track range mode is enabled a third byte should be read in the Result Phase which will indicate the four most signifi- cant bits of the present track number Otherwise only two result bytes should be read 27 |
Similar Part No. - PC8477BV-1 |
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Similar Description - PC8477BV-1 |
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