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HOST SOFTWARE INTERFACE
6 – 5
Control Diagnostic RegistersControl Diagnostic Registers
Control Diagnostic RegistersControl Diagnostic Registers
Control Diagnostic Registers
These I/O port addresses reference three Control/Diagnostic registers:
I/O PORT READ WRITE
3F6h Alternate Status Fixed Disk Control
3F7h Digital Input Not used
Alternate Status RegisterAlternate Status Register
Alternate Status RegisterAlternate Status Register
Alternate Status Register
Contains the same information as the Status register in the Task File. However, this register may be read at
any time without clearing a pending interrupt.
Device Control RegisterDevice Control Register
Device Control RegisterDevice Control Register
Device Control Register
Contains the software Reset and Enable bit to enable interrupt requests to the host. Bit definitions follow:
76543210
00000SRSTIEN0
Reset IRQ Enable
Reset – Setting the software Reset bit holds the drive in the reset state. Clearing the bit re-enables the drive.
The software Reset bit must be held active for a minimum of 5 µsec.
IRQ Enable – Setting the Interrupt Request Enable to 0 enables the IRQ 14 signal to the host. When this
bit is set to 1, IRQ14 is tri-stated, and interrupts to the host are disabled. Any pending interrupt occurs when
the bit is set to 0. The default state of this bit after power up is 0 (interrupt enabled).
Digital Input RegisterDigital Input Register
Digital Input RegisterDigital Input Register
Digital Input Register
Contains information about the state of the drive. Bit definitions follow:
76543210
x -WG -HS3 -HS2 -HS1 -HS0 -DS1 DS0
Reserved Write
Gate
Head
Select 3
Head
Select 2
Head
Select 1
Head
Select 0
Drive
Select 1
Drive
Select 0
Bit 7 of the host data bus is not driven when this register is read.
-Write Gate – Reflects the state of the active low write gate signal on the drive.
-Head Select 3 through -Head Select 0 – Represents the ones complement of the currently selected head number.
-Drive Select 1 – Is 0 if drive 1 selected; 1 otherwise.
-Drive Select 0 – Is 0 if drive 0 selected; 1 otherwise.