DP8473N NSC [National Semiconductor], DP8473N Datasheet - Page 19

• Manufacturer Part Number: DP8473N
• Description: DP8473 Floppy Disk Controller PLUS-2
• Manufacturer: NSC [National Semiconductor]

Command Description
SEEK
There are two ways to move the disk drive head to the
desired track number Method One is to enable the Implied
Seek Mode This way each individual Read or Write com-
mand will automatically move the head to the track speci-
fied in the command
Method Two is using the Seek Command During the Execu-
tion Phase of the Seek Command the track number to seek
to is compared with the present track number and a step
pulse is produced to move the head one track closer to the
desired track number This is repeated at the rate specified
by the Specify Command until the head reaches the correct
track At this point an interrupt is generated and a Sense
Interrupt Command is required to clear the interrupt
During the Execution Phase of the Seek Command the only
indication via software that a Seek Command is in progress
is bits 0 –3 (Drive Busy) of the Main Status Register Bit 4 of
the Main Register (Controller Busy) is not set While the
internal microengine is capable of multiple seeks on 2 or
more drives at the same time since the drives are selected
via the Drive Control Register in software software should
ensure that only one drive is seeking at one time No other
command except the Sense Interrupt Command should be
issued while a Seek Command is in progress
If the extended track range mode is enabled a fourth byte
should be written in the Command Phase to indicate the
four most significant bits of the desired track number Other-
wise only three bytes should be written
RECALIBRATE
The Recalibrate Command is very similar to the Seek Com-
mand It is used to step a drive head out to track zero Step
pulses will be produced until the track zero signal from the
drive becomes true If the track zero signal does not go true
before 77 step pulses are issued an error is generated If
the extended track range mode is enabled an error is not
generated until 3917 pulses are issued
Recalibrations on more than one drive at a time should not
be issued for the same reason as explained in the Seek
Command No other command except the Sense Interrupt
Command should be issued while a Recalibrate Command
is in progress
SENSE INTERRUPT STATUS
An interrupt is generated by the controller when any of the
following conditions occur
1 Upon entering the Result Phase of
2 During data transfers in the Execution Phase while in the
3 Internal Ready signal changes state (only occurs imme-
4 Seek or Recalibrate Command termination
An interrupt generated for reasons 1 and 2 above occurs
during normal command operations and are easily discern-
a Read Data Command
b Read Deleted Data Command
c Write Data Command
d Write Deleted Data Command
e Read a Track Command
f Read ID Command
g Format Command
h Scan Commands
Non-DMA mode
diately after a hardware or software reset)
(Continued)
19
ible by the
Mode bit 5 (Execution Mode) in the Main Status Register is
set to 1 Upon entering Result Phase this bit is set to 0
Reasons 1 and 2 do not require the Sense Interrupt Status
command The interrupt is cleared by reading or writing in-
formation to the data register
Interrupts caused by reasons 3 and 4 are identified with the
aid of the Sense Interrupt Status Command This command
resets the interrupt when the command byte is written Use
bits 5 6 and 7 of ST0 to identify the cause of the interrupt as
shown in Table XIII
Issuing a Sense Interrupt Status Command without an inter-
rupt pending is treated as an invalid command
If the extended track range mode is enabled a third byte
should be read in the Result Phase which will indicate the
four most significant bits of the Present Track Number Oth-
erwise only two bytes should be read
SPECIFY
The Specify Command sets the initial values for each of the
three internal timers The timer programming values are
shown in Table XIV
The Head Load and Head Unload timers are artifacts of the
the head until a read or write command is started and un-
loading the head sometime after the command was com-
pleted Since the DP8473’s head load signal is now the soft-
ware controlled Motor lines in the Drive Control Register
these timers only provide some delay from the initiation of a
command until it is actually started These times can be
extended by setting the TMR bit in the Mode Command
The Step Rate Time defines the time interval between adja-
cent step pulses during a Seek Implied Seek or Recali-
brate Command
The times stated in the table are affected by the Data Rate
The values in the table are for 500 kb s MFM (250 kb s FM)
and 1 Mb s MFM (500 kb s FM) For a 300 kb s MFM data
rate (150 kb s FM) these values should be multiplied by
1 6667 and for 250 kb s MFM (125 kb s FM) these values
should be doubled
The choice of DMA or Non-DMA operation is made by the
NON-DMA bit When this bit is 1 then Non-DMA mode is
selected and when this bit is 0 the DMA mode is selected
This command does not generate an interrupt
Step Rate (16
Motor Off
Motor On
PD765A These timers determine the delay from loading
Timer
D7
TABLE XIII Status Register 0 Termination Codes
1
0
0
Interrupt
TABLE XIV Step Head Load and Unload Timer
Status Register 0
Code
D6
N2
1
0
1
N3
P During an execution phase in Non-DMA
Value
Definitions (500 kb s MFM)
b
c
c
Mode 1
N1)
16
2
Seek
End
D5
0
1
1
Range
0– 240 N2
0– 254
1– 16
Internal Ready Went True
Normal Seek Termination
Abnormal Seek Termination
(16
N3
Value
c
b
c
Mode 2
512 0– 7680
N1)
32
Cause
0 – 4064
Range
1– 16
Unit
ms
ms
ms