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Transcend Information Inc.

Ver 1.2

11

DMA data-out burst.

During an Ultra DMA data burst a sender shall always drive data onto the bus, and, after a sufficient

time to allow for propagation delay, cable settling, and setup time, the sender shall generate a STROBE

edge to latch the data. Both edges of STROBE are used for data transfers so that the frequency of

STROBE is limited to the same frequency as the data.

Words in the IDENTIFY DEVICE data indicate support of the Ultra DMA feature and the Ultra DMA

modes the device is capable of supporting. The Set transfer mode subcommand in the SET FEATURES

command shall be used by a host to select the Ultra DMA mode at which the system operates. The Ultra

DMA mode selected by a host shall be less than or equal to the fastest mode of which the device is

capable. Only one Ultra DMA mode shall be selected at any given time. All timing requirements for a

selected Ultra DMA mode shall be satisfied. Devices supporting any Ultra DMA mode shall also support

all slower Ultra DMA modes.

An Ultra DMA capable device shall retain the previously selected Ultra DMA mode after executing a

software reset sequence or the sequence caused by receipt of a DEVICE RESET command if a SET

FEATURES disable reverting to defaults command has been issued. The device may revert to a

Multiword DMA mode if a SET FEATURES enable reverting to default has been issued. An Ultra DMA

capable device shall clear any previously selected Ultra DMA mode and revert to the default non-Ultra

DMA modes after executing a power-on or hardware reset.

Both the host and device perform a CRC function during an Ultra DMA data burst. At the end of an

Ultra DMA data burst the host sends its CRC data to the device. The device compares its CRC data to

the data sent from the host. If the two values do not match, the device reports an error in the error register.

If an error occurs during one or more Ultra DMA data bursts for any one command, the device shall report

the first error that occurred. If the device detects that a CRC error has occurred before data transfer for

the command is complete, the device may complete the transfer and report the error or abort the

command and report the error.

NOTE

− If a data transfer is terminated before completion, the assertion of INTRQ should be passed

through to the host software driver regardless of whether all data requested by the command has been

transferred.