NCT6627UD Nuvoton Technology Corporation of America, NCT6627UD Datasheet - Page 102

• Manufacturer Part Number: NCT6627UD
• Manufacturer: Nuvoton Technology Corporation of America

Specifications of NCT6627UD

• Lead Free Status / Rohs Status: Supplier Unconfirmed

9. FLOPPY DISK CONTROLLER
The floppy disk controller (FDC) of the W83627UHG integrates all of the logic required for floppy disk control.
The FDC implements a FIFO, which provides better system performance in multi-master systems, and the digital
data separator supports data rates up to 2 M bits/sec.
The FDC includes the following blocks: Precompensation, Data Rate Selection, Digital Data Separator, FIFO, and
FDC Core. The rest of this section discusses these blocks through the following topics: FIFO, Data Separator,
Write Precompensation, Perpendicular Recording mode, FDC core, FDC commands, and FDC registers.
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 (Request for Master) and DIO
(Data Input/Output) bits in the Main Status Register.
The FIFO is defaulted to disabled mode after any form of reset, which maintains PC/AT hardware compatibility.
The default values can be changed through the configure command. The advantage of the FIFO is that it allows a
larger DMA latency in the system without causing disk errors. The following tables give several examples of the
delays with the FIFO. The data are based upon the following formula:
9.1
9.1.1 FIFO (Data)
FIFO THRESHOLD
FIFO THRESHOLD
FDC Functional Description
15 Byte
15 Byte
1 Byte
2 Byte
8 Byte
1 Byte
2 Byte
8 Byte
DELAY = THRESHOLD # × (1 / DATA RATE) * 8 – 1.5 μs
Table 9-1 The Delays of the FIFO
Data Rate
Data Rate
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
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
1 × 16 μs – 1.5 μs = 14.5 μs
MAXIMUM DELAY UNTIL SERVICING AT 500K BPS
MAXIMUM DELAY UNTIL SERVICING AT 1M BPS
-93-
W83627UHG/NCT6627UD
Publication Release Date: October 26, 2010
Revision 1.7