FLOPPY DISK CONTROLLER
The Floppy Disk Controller (FDC) provides the interface between a host microprocessor and the floppy disk drives. The
FDC integrates the functions of the Formatter/Controller, Digital Data Separator, Write Precompensation and Data Rate
Selection logic for an IBM XT/AT compatible FDC. The true CMOS 765B core guarantees 100% IBM PC XT/AT
compatibility in addition to providing data overflow and underflow protection.
The FDC is compatible to the 82077AA using
SMSC's proprietary floppy disk controller core.
FDC INTERNAL REGISTERS
The Floppy Disk Controller contains eight internal registers which facilitate the interfacing between the host
microprocessor and the disk drive. Table 2 shows the addresses required to access these registers. Registers other
than the ones shown are not supported. The rest of the description assumes that the primary addresses have been
selected.
Table 2 - Status, Data and Control Registers
(Shown with base addresses of 3F0 and 370)
PRIMARY
ADDRESS
3F0
SECONDARY
ADDRESS
370
R/W
R
REGISTER
Status Register A (SRA)
Status Register B (SRB)
Digital Output Register (DOR)
Tape Drive Register (TDR)
Main Status Register (MSR)
Data Rate Select Register (DSR)
Data (FIFO)
3F1
371
R
3F2
372
R/W
R/W
R
3F3
373
3F4
374
3F4
374
W
3F5
375
R/W
3F6
376
Reserved
3F7
377
R
Digital Input Register (DIR)
Configuration Control Register (CCR)
3F7
377
W
STATUS REGISTER A (SRA)
Address 3F0 READ ONLY
This register is read-only and monitors the state of the internal interrupt signal and several disk interface
pins in PS/2 and Model 30 modes. The SRA can be accessed at any time when in PS/2 mode. In the PC/AT mode the
data bus pins D0 - D7 are held in a high impedance state for a read of address 3F0.
PS/2 Mode
7
INT
6
5
4
3
2
1
0
nDRV2 STEP nTRK0 HDSEL nINDX nWP
DIR
PENDING
0
RESET
COND.
1
0
N/A N/A N/A
0
0
BIT 0 DIRECTION
Active high status indicating the direction of head movement. A logic "1" indicates inward direction; a logic "0" indicates
outward direction.
BIT 1 nWRITE PROTECT
Active low status of the WRITE PROTECT disk interface input. A logic "0" indicates that the disk is write protected.
BIT 2 nINDEX
Active low status of the INDEX disk interface input.
BIT 3 HEAD SELECT
Active high status of the HDSEL disk interface input. A logic "1" selects side 1 and a logic "0" selects side 0.
SMSC LPC47B27x
- 23 -
Rev. 08-10-04
DATASHEET
SMSC [ SMSC CORPORATION ]
