
7.4 Floppy Disk Controller 
SMSC DS – LPC47M192 
Page 31 
Rev. 03/30/05 
DATASHEET 
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.  LPC47M192 supports two floppy drive directly (see “Direct Support for Two Floppy Drives” 
subsection). 
The FDC is compatible to the 82077AA using SMSC’s proprietary floppy disk controller core. 
7.4.1 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 
3F1 
3F2 
3F3 
3F4 
3F4 
3F5 
3F6 
3F7 
3F7 
STATUS REGISTER A (SRA) 
Address 3F0 READ ONLY
SECONDARY 
ADDRESS
370 
371 
372 
373 
374 
374 
375 
376 
377 
377 
R/W
REGISTER
R 
R 
R/W 
R/W 
R 
W 
R/W 
R 
W 
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) 
Reserved  
Digital Input Register (DIR) 
Configuration Control Register (CCR) 
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 
6 
5 
4 
INT 
PENDIN
G 
RESET 
COND. 
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. 
3 
2 
1 
0 
nDRV2 
STEP 
nTRK0 
HDSEL 
nINDX 
nWP 
DIR 
0 
1 
0 
N/A 
0 
N/A 
N/A 
0