W83627HF Datasheet, PDF (31/185 Pages) Winbond – WINBOND I/O

W83627HF/F
PRELIMINARY
3. FDC FUNCTIONAL DESCRIPTION
3.1 W83627HF FDC
The floppy disk controller of the W83627HF integrates all of the logic required for floppy disk control.
The FDC implements a PC/AT or PS/2 solution. All programmable options default to compatible
values. The FIFO provides better system performance in multi-master systems. The digital data
separator supports up to 2 M bits/sec data rate.
The FDC includes the following blocks: AT interface, Precompensation, Data Rate Selection, Digital
Data Separator, FIFO, and FDC Core.
3.1.1 AT interface
The interface consists of the standard asynchronous signals: _RD#, WR#, A0-A3, IRQ, DMA control, and
a data bus. The address lines select between the configuration registers, the FIFO and control/status
registers. This interface can be switched between PC/AT, Model 30, or PS/2 normal modes. The PS/2
register sets are a superset of the registers found in a PC/AT.
3.1.2 FIFO (Data)
The FIFO is 16 bytes in size and has programmable threshold values. All command parameter
information and disk data transfers go through the FIFO. Data transfers are governed by the RQM and
DIO bits in the Main Status Register.
The FIFO defaults to disabled mode after any form of reset. This maintains PC/AT hardware
compatibility. The default values can be changed through the CONFIGURE command. The advantage
of the FIFO is that it allows the system a larger DMA latency without causing disk errors. The following
tables give several examples of the delays with a FIFO. The data are based upon the following formula:
THRESHOLD # × (1/DATA/RATE) *8 - 1.5 µS = DELAY
FIFO THRESHOLD
MAXIMUM DELAY TO SERVICING AT 500K BPS
1 Byte
2 Byte
8 Byte
15 Byte
Data Rate
1 × 16 µS - 1.5 µS = 14.5 µS
2 × 16 µS - 1.5 µS = 30.5 µS
8 × 16 µS - 1.5 µS = 6.5 µS
15 × 16 µS - 1.5 µS = 238.5 µS
FIFO THRESHOLD
1 Byte
2 Byte
8 Byte
15 Byte
MAXIMUM DELAY TO SERVICING AT 1M BPS
Data Rate
1 × 8 µS - 1.5 µS = 6.5 µS
2 × 8 µS - 1.5 µS = 14.5 µS
8 × 8 µS - 1.5 µS = 62.5 µS
15 × 8 µS - 1.5 µS = 118.5 µS
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Publication Release Date: Jul 1999
Revision 0.53