User Manual

ATA Command Description

CompactFlash

5.1.10. Read Multiple—C4H

Table 5-13. Read Multiple

Bit -> 7 6 5 4 3 2 1 0

Command (7) C4H

C/D/H (6) 1 LBA 1 Drive Head (LBA 27-24)

Cyl High (5) Cylinder High (LBA 23-16)

Cyl Low (4) Cylinder Low (LBA 15-8)

Sec Num (3) Sector Number (LBA 7-0)

Sec Cnt (2) Sector Count

Feature (1) X

NOTE: The current revision of the CompactFlash Memory Card only supports a block count of 1 as indicated in

the Identify Drive Information command. This command is provided for compatibility with future products

that may support a larger block count.

The Read Multiple command performs similarly to the Read Sectors command. Interrupts are not generated on

every sector, but on the transfer of a block, which contains the number of sectors defined by a Set Multiple,

command.

Command execution is identical to the Read Sectors operation except that the number of sectors defined by a Set

Multiple command is transferred without intervening interrupts. DRQ qualification of the transfer is required only at

the start of the data block, not on each sector.

The block count of sectors to be transferred without intervening interrupts is programmed by the Set Multiple Mode

command, which must be executed prior to the Read Multiple command. When the Read Multiple command is

issued, the Sector Count Register contains the number of sectors (not the number of blocks or the block count)

requested. If the number of requested sectors is not evenly divisible by the block count, as many full blocks as

possible are transferred, followed by a final, partial block transfer. The partial block transfer is for n sectors, where:

n = (sector count)—modulo (block count).

If the Read Multiple command is attempted before the Set Multiple Mode command has been executed or when

Read Multiple commands are disabled, the Read Multiple operation is rejected with an Aborted Command error.

Disk errors encountered during Read Multiple commands are posted at the beginning of the block or partial block

transfer, but DRQ is still set and the data transfer will take place as it normally would, including transfer of

corrupted data, if any.

Interrupts are generated when DRQ is set at the beginning of each block or partial block. The error reporting is the

same as that on a Read Sector(s) Command. This command reads from 1 to 256 sectors as specified in the Sector

Count register. A sector count of 0 requests 256 sectors. The transfer begins at the sector specified in the Sector

Number Register.

At command completion, the Command Block Registers contain the cylinder, head and sector number of the last

sector read.

If an error occurs, the read terminates at the sector where the error occurred. The Command Block Registers contain

the cylinder, head and sector number of the sector where the error occurred. The flawed data is pending in the sector

buffer.