FDC37B72X(1999) View Datasheet(PDF) - SMSC -> Microchip
Part Name
Description
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FDC37B72X Datasheet PDF : 244 Pages
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until the last transfer (independent of nDACK).
See timing diagrams for more information.
Burst mode is enabled via Bit[1] of CRF0 in
Logical Device 0. Setting Bit[1]=0 enables burst
mode; the default is Bit[1]=1, for non-burst
mode.
CONTROLLER PHASES
For simplicity, command handling in the FDC
can be divided into three phases: Command,
Execution, and Result. Each phase is described
in the following sections.
Command Phase
After a reset, the FDC enters the command
phase and is ready to accept a command from
the host. For each of the commands, a defined
set of command code bytes and parameter
bytes has to be written to the FDC before the
command phase is complete. (Please refer to
TABLE 20 for the command set descriptions).
These bytes of data must be transferred in the
order prescribed.
Before writing to the FDC, the host must
examine the RQM and DIO bits of the Main
Status Register. RQM and DIO must be equal
to "1" and "0" respectively before command
bytes may be written. RQM is set false by the
FDC after each write cycle until the received
byte is processed. The FDC asserts RQM again
to request each parameter byte of the command
unless an illegal command condition is
detected. After the last parameter byte is
received, RQM remains "0" and the FDC
automatically enters the next phase as defined
by the command definition.
The FIFO is disabled during the command
phase to provide for the proper handling of the
"Invalid Command" condition.
Execution Phase
All data transfers to or from the FDC occur
during the execution phase, which can proceed
in DMA or non-DMA mode as indicated in the
Specify command.
After a reset, the FIFO is disabled. Each data
byte is transferred by an FINT or FDRQ
depending on the DMA mode. The Configure
command can enable the FIFO and set the
FIFO threshold value.
The following paragraphs detail the operation of
the FIFO flow control. In these descriptions,
<threshold> is defined as the number of bytes
available to the FDC when service is requested
from the host and ranges from 1 to 16. The
parameter FIFOTHR, which the user programs,
is one less and ranges from 0 to 15.
A low threshold value (i.e. 2) results in longer
periods of time between service requests, but
requires faster servicing of the request for both
read and write cases. The host reads (writes)
from (to) the FIFO until empty (full), then the
transfer request goes inactive. The host must
be very responsive to the service request. This
is the desired case for use with a "fast" system.
A high value of threshold (i.e. 12) is used with a
"sluggish" system by affording a long latency
period after a service request, but results in
more frequent service requests.
Non-DMA Mode - Transfers from the FIFO to
the Host
The FINT pin and RQM bits in the Main Status
Register are activated when the FIFO contains
(16-<threshold>) bytes or the last bytes of a full
sector have been placed in the FIFO. The FINT
pin can be used for interrupt-driven systems,
and RQM can be used for polled systems. The
host must respond to the request by reading
data from the FIFO. This process is repeated
until the last byte is transferred out of the FIFO.
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