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Preliminary CompactFlash Memory Card Product Manual

6.1.10 Read Multiple - C4H

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)

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 which 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

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.

Subsequent blocks or partial blocks are transferred

only if the error was a correctable data error. All

other errors cause the command to stop after

transfer of the block which contained the error.