Intel mcs-48 manual Recalibrate, Sense Interrupt Status, Specify, Sense Drive Status, Invalid

8272

RECALIBRATE

This command causes the read/write head within the FDD to retract to the Track 0 position. The FDC clears the contents of the PCN counter, and checks the status of the Track 0 signal from the FDD. As long as the Track osignal is low, the Direction signal remains 1 (high) and Step Pulses are issued. When the Track 0 signal goes high, the SE (SEEK END) flag in Status Register 0 is set to a 1 (high) and the command is terminated. If the Track o signal is still low after 77 Step Pulses have been· issued, the FDC sets the SE (SEEK END) and EC (EQUIP· MENT CHECK) flags of Status Register 0 to both 1s (highs), and terminates the command.

The ability to overlap RECALIBRATE Commands to multiple FDDs, and the loss of the READY signal, as described in the SEEK Command, also applies to the RECALIBRATE Command.

SENSE INTERRUPT STATUS

An Interrupt signal is generated by the FOC for one of the following reasons:

1.Upon entering the Result Phase of:

a.Read Data Command

b.Read a Track Command

c.Read 10 Command

d.Read Deleted Oata Command

e.Write Data Command

f.Format a Cylinder Command

g.Write Deleted Data Command

h.Scan Commands

2.Ready Line of FOO changes state

3.End of Seek or Recalibrate Command

4.During Execution Phase in the NON·OMA Mode

Interrupts caused by reasons 1 and 4 above occur during normal command operations and are easily discernible by the processor. However, interrupts caused by reasons 2 and 3 above may be uniquely identified with the aid of the Sense Interrupt Status Command. This command when issued resets the interrupt signal and via bits 5, 6, and 7 of Status Register 0 identifies the cause of the interrupt.

TABLE 7. SEEK, INTERRUPT CODES
SEEK END	INTERRUPT CODE		CAUSE
BIT 5	BIT6	BIT7
0	1	1	Ready Line changed
			state, either polarity
1	0	0	Normal Termination
			of Seek or Recalibrate
			Command
1	1	0	Abnormal Termination of
			Seek or Recalibrate
			Command

Neither the Seek or Recalibrate Command have a Result Phase. Therefore, it is mandatory to use the Sense Inter· rupt Status Command after these commands to effec, tively terminate them and to provide verification of the head position (PCN).

SPECIFY

The Specify Command sets the initial values for each of the three internal timers. The HUT (Head Unload Time) defines the time from the end of the Execution Phase of one of the Read/Write Commands to the head unload state. This timer is programmable from 16 to 240 ms in increments of 16 ms (01 = 16 ms, 02 = 32 ms .... OF =

240 ms). The SRT (Step Rate Time) defines the time in· terval between adjacent step pulses. This timer is pro· grammable from 1 to 16 ms in increments of 1 ms (F = 1 ms, E = 2 ms, 0 = 3 ms, etc.). The HLT (Head Load Time) defines the time between when the Head load signal goes high and when the Read/Write operation starts. This timer is programmable from 2 to 254 ms in in· crements of 2 ms (01 = 2 ms, 02 = 4 ms, 03 = 6 ms ....

FE=254 ms).

The time intervals mentioned above are a direct function of the clock (ClK on pin 19). Times indicated above are for an 8 MHz clock, if the clock was reduced to 4 MHz (mini·floppy application) then all time intervals are in· creased by a factor of 2.

The choice of OMA or NON·DMAoperation is made by the NO (NON·OMA)bit. When this bit is high (NO = 1) the NON·OMAmode is selected, and when NO = 0 the DMA mode is selected.

SENSE DRIVE STATUS

This command may be used by the processor whenever it wishes to obtain the status of the FDOs. Status Register 3 contains the Drive Status information.

INVALID

If an invalid command is sent to the FOC (a command not defined above), then the FDC will terminate the com· mand. No interrupt is generated by the 8272 during this condition. Bit 6 and bit 7 (010 and RQM) in the Main Status Register are both high ("1") indicating to the processor that the 8272 is in the Result Phase and the contents of Status Register 0 (STO) must be read. When the processor reads Status Register 0 it will find a 80H indicating an invalid command was received.

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 com· mand as a No·Opcommand, to place the FOC in a stand· by or no operation state.

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