pc8477b National Semiconductor Corporation, pc8477b Datasheet - Page 19

• Manufacturer Part Number: pc8477b
• Description: Advanced Floppy Disk Controller
• Manufacturer: National Semiconductor Corporation

4 0 Command Set Description
4 2 COMMAND DESCRIPTION
4 2 1 Configure Command
The Configure Command will control some operation modes
of the controller It should be issued during the initialization
of the PC8477B after power up The function of the bits in
the Configure registers is described below These bits are
set to their default values after a hardware reset The value
of each bit after a software reset is explained The default
value of each bit is denoted by a ‘‘bullet’’ to the left of each
item
EIS Enable Implied Seeks Default after a software reset

FIFO Enable FIFO for Execution Phase data transfers De-
fault after a software reset if the LOCK bit is 0 If the LOCK
bit is 1 then the FIFO bit will retain its previous value after a
software reset

POLL Disable for Drive Polling Mode Default after a soft-
ware reset

THRESH The FIFO threshold in the Execution Phase of
read and write data transfers Programmable from 00 to 0F
hex Defaults to 00 after a software reset if the LOCK bit is
0 If the LOCK bit is 1 then THRESH will retain its value A
high value of THRESH is suited for slow response systems
and a low value of THRESH is better for fast response sys-
tems
PRETRK Starting track number for write precompensation
Programmable from track 0 (‘‘00’’) to track 255 (‘‘FF’’) De-
faults to track 0 (‘‘00’’) after a software reset if the LOCK bit
is 0 If the LOCK bit is 1 then PRETRK will retain its value
0
1
0
1
0
1
e
e
e
e
e
e
Implied seeks disabled through Configure command
Implied seeks can still be enabled through the Mode
command when EIS
Implied seeks enabled for a read write scan or veri-
fy operation A seek and sense interrupt operation
will be performed prior to the execution of the read
write scan or verify operation The IPS bit does not
need to be set
FIFO enabled for both reads and writes
FIFO disabled (default)
Enable polling mode An interrupt is generated after
a reset (default)
Disable drive polling mode If the Configure com-
mand is issued within 500 ms of a hardware or soft-
ware reset then an interrupt will not be generated In
addition the four Sense Interrupt commands to clear
the ‘‘Ready Changed State’’ of the four logical drives
will not be required
e
0 (default)
(Continued)
19
4 2 2 Dumpreg Command
The Dumpreg command is designed to support system run-
time diagnostics and application software development and
debug This command has a one byte command phase and
a ten byte result phase which return the values of parame-
ters set in other commands That is the PTR (Present Track
Register) contains the least significant byte of the track the
microcode has stored for each drive The Step Rate Time
Motor Off and Motor On Times and the DMA bit are all set
in the Specify command
The sixth byte of the result phase varies depending on
which commands have been previously executed If a for-
mat command has previously been issued and no reads or
writes have been issued since then then this byte will con-
tain the Sectors per track value If a read or a write com-
mand has been executed more recently than a format com-
mand this byte will contain the End of Track value The
LOCK bit is set in the Lock command The eighth result byte
also contains the bits programmed in the Perpendicular
Mode command The last two bytes of the Dumpreg Result
Phase are set in the Configure command After a hardware
or software reset the parameters in the result bytes will be
set to their appropriate default values
Note Some of these parameters are unaffected by a software reset de-
4 2 3 Format Track Command
This command will format one track on the disk in IBM ISO
or Perpendicular Format After the index hole is detected
data patterns are written on the disk including all Gaps Ad-
dress Marks Address Fields and Data Fields The exact
format is determined by the following parameters
1 The MFM bit in the Opcode (first command) byte which
2 The IAF bit in the Mode command which selects be-
3 The WGATE and GAP bits in the Perpendicular Mode
4 The Bytes per Sector code which determines the sector
5 The Sectors per Track parameter which determines how
6 The Data Pattern byte which is used as the filler byte in
To allow for flexible formatting the mP must supply the four
Address Field bytes (track head sector bytes per sector
code) for each sector formatted during the Execution
Phase This allows for non-sequential sector interleaving
This transfer of bytes from the mP to the controller can be
done in the DMA or Non-DMA mode with the FIFO enabled
or disabled
determines the format of the Address Marks and the en-
coding scheme
tween IBM and ISO format
command which select between the conventional and
Toshiba Perpendicular format
size
many sectors will be formatted on the track
the Data Field of each sector
pending on the state of the LOCK bit