FDC37M817-MS Standard Microsystems (SMSC), FDC37M817-MS Datasheet - Page 64

• Manufacturer Part Number: FDC37M817-MS
• Manufacturer: Standard Microsystems (SMSC)

Specifications of FDC37M817-MS

• Pin Count: 100
• Lead Free Status / RoHS Status: Compliant

Configure
The Configure command is issued to select the
special features of the FDC.
command need not be issued if the default values
of the FDC meet the system requirements.
Configure Default Values:
EIS - No Implied Seeks
EFIFO - FIFO Disabled
POLL - Polling Enabled
FIFOTHR - FIFO Threshold Set to 1 Byte
PRETRK - Pre-Compensation Set to Track 0
EIS - Enable Implied Seek. When set to "1", the
FDC will perform a Seek operation before
executing a read or write command. Defaults to
no implied seek.
EFIFO - A "1" disables the FIFO (default). This
means data transfers are asked for on a byte-by-
byte basis. Defaults to "1", FIFO disabled. The
threshold defaults to "1".
POLL - Disable polling of the drives. Defaults to
"0", polling enabled.
interrupt is generated after a reset. No polling is
performed while the drive head is loaded and the
head unload delay has not expired.
FIFOTHR - The FIFO threshold in the execution
phase of read or write commands. This is
programmable from 1 to 16 bytes. Defaults to one
byte. A "00" selects one byte; "0F" selects 16
bytes.
PRETRK
Number.
Defaults to track 0. A "00" selects track 0; "FF"
selects track 255.
Version
The Version command checks to see if the
controller is an enhanced type or the older type
(765A). A value of 90 H is returned as the result
byte.
Programmable from track 0 to 255.
-
Pre-Compensation
When enabled, a single
A Configure
Start
Track
64
Relative Seek
The command is coded the same as for Seek,
except for the MSB of the first byte and the DIR
bit.
DIR
RCN
The Relative Seek command differs from the Seek
command in that it steps the head the absolute
number of tracks specified in the command
instead of making a comparison against an
internal register. The Seek command is good for
drives that support a maximum of 256 tracks.
Relative Seeks cannot be overlapped with other
Relative Seeks. Only one Relative Seek can be
active at a time. Relative Seeks may be
overlapped with Seeks and Recalibrates. Bit 4 of
Status Register 0 (EC) will be set if Relative Seek
attempts to step outward beyond Track 0.
As an example, assume that a floppy drive has
300 useable tracks. The host needs to read track
300 and the head is on any track (0-255). If a Seek
command is issued, the head will stop at track
255. If a Relative Seek command is issued, the
FDC will move the head the specified number of
tracks, regardless of the internal cylinder position
register (but will increment the register). If the head
was on track 40 (d), the maximum track that the
FDC could position the head on using Relative
Seek will be 295 (D), the initial track + 255 (D).
The maximum count that the head can be moved
with a single Relative Seek command is 255 (D).
The internal register, PCN, will overflow as the
cylinder number crosses track 255 and will contain
39 (D). The resulting PCN value is thus (RCN +
PCN) mod 256. Functionally, the FDC starts
Relative Cylinder Number that determines
how many tracks to step the head in or out
from the current track number.
Head Step Direction Control
DIR
0
1
Step Head Out
Step Head In
ACTION