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11.5 Ultra DMA
Ultra DMA protocol is used with Read DMA, and Write DMA commands. Ultra DMA modes are set by Set
features command. Since the setting after power-up ( Default setting ) is mode 2 of Multi Word DMA, Set
Features command shall be issued to be used in Ultra DMA mode.
An Ultra DMA data transfer is accomplished through a series of Ultra DMA data in or data out bursts. Each
Ultra DMA burst has three mandatory phases of operation: the initiation phase, the data transfer phase, and
the Ultra DMA burst termination phase. An Ultra DMA burst is defined as the period from an assertion of
DMACK- by the host to the subsequent negation of DMACK-. A recipient shall be prepared to receive at
least 2 data words.
Both the host and drive perform a CRC function during an Ultra DMA burst. At the end of an Ultra DMA
burst, the drive compares its CRC data to the data sent from the host. The drive requires an Ultra DMA
burst termination for each sector to compare CRC data to the data sent from the host.
1. Initiation phase
a) An Ultra DMA burst initiation phase begins with the assertion of DMARQ by the drive and ends when the
sender generates a STROBE edge to transfer the first data word.
b) An Ultra DMA burst is always requested by a drive asserting DMARQ.
c) A host indicates it is ready to initiate the requested Ultra DMA burst by asserting DMACK-.
d) A host shall never assert DMACK- without first detecting that DMARQ is asserted.
e) For Ultra DMA data in bursts: a drive may begin driving DD(15:0) after detecting that DMACK- is
asserted, STOP negated, and HDMARDY- is asserted.
f) After asserting DMARQ or asserting DDMARDY- for an Ultra DMA data out burst, the shall not negate
either signal until the first STROBE edge is generated.
g) After negating STOP or asserting HDMARDY- for an Ultra DMA data in burst, a host shall not change the
state of either signal until the first STROBE edge is generated.
2. Data transfer phase
a) The data transfer phase is in effect from after Ultra DMA burst initiation until Ultra DMA burst termination.
b) A recipient pauses an Ultra DMA burst by negating DMRDY- and resumes an Ultra DMA burst by
reasserting DMARDY-.
c) A sender pauses an Ultra DMA burst by not generating STROBE edges and resumes by generating
STROBE edges.
d) A recipient must not signal a termination request when a sender stops generating STROBE edges. In the
absence of a termination from the sender, the recipient should always negate DMARDY- and wait the
required period before signaling a termination request.
e) A sender may generate STROBE edges at greater than the minimum period specified by the enabled
Ultra DMA Mode . The sender should not generate STROBE edges at less than the minimum period
specified by the abled Ultra DMA Mode. A recipient should be able to receive data at the minimum
period specified by the enabled Ultra DMA Mode.
