82077AA Datasheet, PDF (42/62 Pages) Intel Corporation – CHMOS SINGLE-CHIP FLOPPY DISK CONTROLLER

82077AA
As a note if the CONFIGURE command is issued
within 250 ms of the trailing edge of reset ( 1
Mbps) the polling mode of the 82077AA can be dis-
abled before the polling initiated interrupt occurs
Since polling stops when the 82077AA enters the
command phase it is only time critical up to the first
byte of the CONFIGURE command If disabled in
time the system software no longer needs to issue
the four SENSE INTERRUPT STATUS commands
to clear the internal interrupt flags normally caused
by polling
The CONFIGURE command should also be issued if
the system requirements are different from the de-
fault settings (as described in Section 5 2 7) For ex-
ample the CONFIGURE command can be used to
enable the FIFO set the threshold and enable Im-
plied Seeks
The non-DMA mode flag step rate (SRT) head load
(HLT) and head unload times (HUT) programmed by
the SPECIFY command do not default to a known
state after a reset This behavior is consistent with
the 8272A and has been preserved here for compat-
ibility Thus it is necessary to always issue a SPECI-
FY command in the initialization routine
8 3 Recalibrates and Seeks
Commands that position the disk head are different
from the typical READ WRITE FORMAT command
in the sense that there is no result phase Once a
RECALIBRATE SEEK or RELATIVE SEEK com-
mand has been issued the 82077AA will return a
ready status in the Main Status Register (MSR) and
perform the head positioning operation as a back-
ground task When the seek is complete the
82077AA will assert the INT signal to request serv-
ice A SENSE INTERRUPT STATUS command
should then be asserted to clear the interrupt and
read the status of the operation Since the drive and
motor enable signals are directly controlled through
the Digital Output Register (DOR) on the 82077AA
a write to the DOR will need to precede the RECALI-
BRATE or SEEK command if the drive and motor is
not already enabled Figure 8-4 shows the flow chart
for this operation
Figure 8-4 Recalibrate and Seek Operations
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