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Chapter 5 Input/Output Interfaces
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition – September 1997
5-6
Command Register, I/O Port 1F7h/177h (Write Only)
The IDE controller commands are written to this register. The command write action should be
prefaced with the loading of data into the appropriate registers. Execution begins when the
command is written to 1F7h/177h. Table 5-4 lists the standard IDE commands.
Table 5–4. IDE Controller Commands
Table 5-4.
IDE Controller Commands
Command Value
Initialize Drive Parameters 91h
Seek 7xh
Recalibrate 1xh
Read Sectors with Retries 20h*
Read Long with Retries 22h*
Write Sectors with Retries 30h*
Write Long with Retries 32h*
Verify Sectors with Retries 40h
Format Track 50h
Execute Controller Diagnostic 90h
Idle 97h, E3h
Idle Immediate 95h, E1h
Enter Low Power and Enable/Disable Timeout 96h
Enter Idle and Enable/Disable Timeout 97h
Check Status 98h
Identify ECh
Read Buffer E4h
Write Buffer E8h
NOP 00h
Read DMA with Retry C8h
Read DMA without Retry C9h
Read Multiple C4h
Set Features EFh
Set Multiple Mode C6h
Sleep 99h, E6h
Standby 96h, E2h
Standby Immediate 94h, E0h
Write DMA with Retry CAh
Write DMA without Retry CBh
Write Multiple C5h
Write Same E9h
Write Verify 3Ch
* Without retries, add one to the value.
Alternate Status Register, I/O Port 3F6h/376h (Read Only)
The alternate Status register at location 3F6h holds the same status data as location 1F7h but
does not clear hardware conditions when read.