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8272
SINGLE/DOUBLE DENSITY
FLOPPY DISK CONTROLLER

&amstrad; The 8272 is a LSI Floppy Disk Controller (FDC) Chip, which contains the curcuitry and control functions for interfacing a processor to 4 Floppy Disk Drives. It is capable of supporting either IBM 3740 single density format (FM), or IBM System 34 Double Density format (MFM) including double sided recording. The 8272 provides control signals which simplify the design of an external phase locked loop, and write precompensation circuitry. The FDC simplifies and handles most of the burdens associated with implementing a Floppy Disk Drive Interface.

PIN CONFIGURATION

[8272 Pin configuration]

8272 INTERNAL BLOCK DIAGRAM

[8272 Internal Block Diagram]

8272 SYSTEM BLOCK DIAGRAM


A Sense Interrupt Status Command must be sent after a Seek or Recalibrate interrupt, otherwise the FDC will consider the next command to be an Invalid Command.

In some applications the user may wish to use this command as a No-Op command, to place the FDC in a standby or no operation state.

TABLE 8. STATUS REGISTERS


STATUS REGISTER 0
Bit No. Name Symbol Description
D7,D6Interrupt CodeIC
D7=0 and D6=0; Normal Termination of Command (NT), Command was completed and properly executed.
D7=0 and D6=1; Abnormal Termination of Command (AT), Execution of Command was started, but was not successfully completed.
D7=1 and D6=0; Invalid Command issued (IC), Command which was issued was never started.
D7=1 and D6=1; Abnormal Termination because during command execution the ready signal from the FDD changed state.
D5Seek EndSEWhen the FDC completes the SEEK command, this flag is set to 1 (high).
D4Equipment CheckECIf a fault signal is received from the FDD, or if the Track 0 signal fails to occur after 77 Step Pulses (Recalibrate Command) then this flag is set.
D3Not ReadyNRWhen the FDD is in the not-ready state and a read or write command is issued, this flag is set. If a read or write command is issued to Side 1 of a single sided drive then this flag is set.
D2Head AddressHDThis flag is used to indicate the state of the head at interrupt.
D1Unit Select 1US 1 These flags are used to indicate the drive unit number at interrupt.
D0Unit Select 0US 0




STATUS REGISTER 1
Bit No. Name Symbol Description
D7End of CylinderENWhen the FDC tries to access a sector beyond the final Sector of a Cylinder, this flag is set.
D6Not used. This bit is always 0 (low).
D5Data ErrorDEWhen the FDC detects a CRC error in either the ID field or the data field, this flag is set.
D4Over RunORIf the FDC is not serviced by the main systems during data transfers within a certain time interval, this flag is set.
D3Not used. This bit always 0 (low).
D2No DataND
During execution of READ DATA, WRITE DELETED DATA or SCAN Command, if the FDC cannot find the Sector specified in the IDR register, then this flag is set.
During executing the READ ID Command, if the FDC cannot read the ID field without an error, then this flag is set.
During execution of the READ A Cylinder Command, if the starting sector cannot be found then this flag is set.
D1Not WriteableNWDuring execution of WRITE DATA, WRITE DELETED DATA or Format a Cylinder Command, if the FDC detects a write protect signal from the FDD, then this bit is set.
D0Missing Address MarkMA
If the FDC cannot detect the ID Address Mark after encountering the index hole twice, then this flag is set.
If the FDC cannot detect the Data Address Mark or the Deleyed Data Address Mark, this flag is set. Also at the same time, the MD (Missing Address Mark in Data Field) of Status Register is set.




STATUS REGISTER 2
Bit No. Name Symbol Description
D7Not used. This bit is always 0 (low).
D6Control MarkCMDuring executing the READ DATA or SCAN Command, if the FDC encounters a Sector which contains a Deleted Data Address Mark, this flag is set.
D5Data Error in Data FieldDDIf the FDC detects a CRC error in the data field then this flag is set.
D4Wrong CylinderWCThis bit is related with the ND bit, and when the contents of C on the medium is different from that stored in the IDR, this flag is set.
D3Scan Equal HitSHDuring execution, the SCAN Command, if the condition of the "equal" is satisfied, then this flag is set.
D2Scan Not SatisfiedSNDuring executing the SCAN Command, if the FDC cannot find a sector on the cylinder which meets the condition, then this flag is set.
D1Bad CylinderBCThis bit is related with the ND bit and when the contents of C on the mdeium is different from that stored in the IDR and the content of C is &FF, then this flag is set.
D0Missing Address Mark in Data FieldMDWhen data is read from the medium, if the FDC cannot find a Data Address Mark or Deleted Data Address Mark, then this flag is set.




STATUS REGISTER 3
Bit No. Name Symbol Description
D7FaultFTThis bit is used tto indicate the status of the Fault signal from the FDD.
D6Write ProtectedWPThis bit is used to indicate the status of the Write Protected signal from the FDD.
D5ReadyRDYThis bit is used to indicate the status of the Ready signal from the FDD.
D4Track 0T0This bit is used to indicate the status of the Track 0 signal from the FDD.
D3Two SideTSThis bit is used to indicate the status of the Two Side signal from the FDD.
D2Head AddressHDThis bit is used to indicate the status of the Side Select signal to the FDD.
D1Unit Select 1US 1This bit is used to indicate the status of the Unit Select 1 signal to the FDD.
D0Unit Select 0US 0This bit is used to indicate the status of the Unit Select 0 signal to the FDD.