Host Software Interface, Task File Registers

HOST SOFTWARE INTERFACE

SECTION 6

Host Software Interface

The host communicates with the drive through a set of controller registers accessed via the host’s I/O ports. These registers divide into two groups: the Task File, used for passing commands and command parameters and the Control/Diagnostic registers.

Task File Registers

The Task File consists of eight registers used to control fixed disk operations. The host accesses each register by the I/O port address shown in this Task File register map:

I/O PORT	READ	WRITE
1F0h	Data Register	Data Register
1F1h	Error Register	Features Register
1F2h	Sector Count	Sector Count
1F3h	Sector Number	Sector Number
1F4h	Cylinder Low	Cylinder Low
1F5h	Cylinder High	Cylinder High
1F6h	Drive/Head (SDH)	Drive/Head (SDH)
1F7h	Status Register	Command Register

Data Register

Provides access to the drive’s sector buffer for read and write operations. With the exception of ECC byte transfers (which, during Read long and Write long commands, are 8 bits wide), data transfers through the Data register are all 16 bits wide.

Error Register

A read-only register containing specific information regarding the previous command. Data interpretation differs depending on whether the controller is in operational or diagnostic mode. A power up, reset, software reset, or receipt of a diagnostic command sets the controller into diagnostic mode. This mode invalidates contents of the Status register. The contents of the Error register reflect a completion code.

Issuing any command (apart from a Diagnostic command) places the controller into operational mode.

In operational mode, the Error register is valid only when the Error bit in the Status register is set. The bit definitions for operational mode follow:

7	6	5	4	3	2	1	0
0	ECC	0	IDNF	0	ABRT	TK0	AMNF

Interface	Data	Not	ID	Not	Aborted	Track 0	Address
CRC	ECC Error	Used	Not Found	Used	Command	Error	Mark Not
							Found

Interface CRC – An interface CRC error occurred during an Ultra DMA transfer.

Data ECC Error – An non-correctable ECC error occurred during a Read Sector command.

Firmware Problem – Indicates a firmware problem was detected, (e.g., invalid interrupt, divide overflow). ID Not Found – Either a matching ID field not found, or a CRC error occurred.

Aborted Command – Invalid commands, write fault, no seek complete, or drive not ready.

Track 0 Error – Track 0 was not found during execution of a Restore command.

Address Mark Not Found – The Address Mark could not be found after an ID match.

Features Register

Enables or disables features through the Set Features command.

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