W83977AF Information Storage Devices, Inc, W83977AF Datasheet - Page 29

• Manufacturer Part Number: W83977AF
• Description: W83877TF Plus Kbc, Cir, RTC
• Manufacturer: Information Storage Devices, Inc

2. FDC FUNCTIONAL DESCRIPTION
2.1 W83977F/ AF FDC
The floppy disk controller of the W83977F/ AF integrates all of the logic required for floppy disk
control.
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.
2.1.1 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.
2.1.2 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:
FIFO THRESHOLD
FIFO THRESHOLD
The FDC implements a PC/AT or PS/2 solution.
15 Byte
15 Byte
1 Byte
2 Byte
8 Byte
1 Byte
2 Byte
8 Byte
THRESHOLD #
(1/DATA/RATE) *8 - 1.5 S = DELAY
1
2
8
15
1
2
8
15
MAXIMUM DELAY TO SERVICING AT 500K BPS
Data Rate
MAXIMUM DELAY TO SERVICING AT 1M BPS
16 S - 1.5 S = 30.5 S
16 S - 1.5 S = 6.5 S
8 S - 1.5 S = 6.5 S
8 S - 1.5 S = 14.5 S
8 S - 1.5 S = 62.5 S
16 S - 1.5 S = 14.5 S
16 S - 1.5 S = 238.5 S
8 S - 1.5 S = 118.5 S
Data Rate
W83977F/ W83977AF
All programmable options default to
Publication Release Date: March 1998
-18-
PRELIMINARY
Revision 0.58