82801CA Datasheet, PDF (378/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

IDE Controller Registers (D31:F1)
10.2.1
BMIC[P,S]—Bus Master IDE Command Register
Address Offset:
Default Value:
Primary: 00h
Secondary: 08h
00h
Attribute:
Size:
R/W
8 bits
Bit
Description
7:4 Reserved. Returns 0s.
Read / Write Control (RWC)—R/W. This bit sets the direction of the bus master transfer. This bit
must NOT be changed when the bus master function is active.
3
0 = Memory reads.
1 = Memory writes.
2:1 Reserved. Returns 0.
Start/Stop Bus Master (START)—R/W.
0 = All state information is lost when this bit is cleared. Master mode operation cannot be stopped
and then resumed. If this bit is reset while bus master operation is still active (i.e., the Bus Master
IDE Active bit of the Bus Master IDE Status register for that IDE channel is set) and the drive has
not yet finished its data transfer (the Interrupt bit in the Bus Master IDE Status register for that
IDE channel is not set), the bus master command is said to be aborted and data transferred from
0
the drive may be discarded instead of being written to system memory.
1 = Enables bus master operation of the controller. Bus master operation begins when this bit is
detected changing from a zero to a one. The controller will transfer data between the IDE device
and memory only when this bit is set. Master operation can be halted by writing a '0' to this bit.
This bit is intended to be cleared by software after the data transfer is completed, as indicated by
either the Bus Master IDE Active bit being cleared or the Interrupt bit of the Bus Master IDE Status
register for that IDE channel being set, or both. Hardware does not clear this bit automatically.
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Intel^® 82801CA ICH3-S Datasheet