參數(shù)資料
型號: 37C669
廠商: SMSC Corporation
英文描述: DIODE SCHOTTKY SINGLE 25V 200mW 0.5V-vf 200mA-IFM 30mA-IF 2uA-IR SOD-323 3K/REEL
中文描述: 電腦98/99順從超級I / O軟盤控制器與紅外線支持
文件頁數(shù): 89/164頁
文件大?。?/td> 621K
代理商: 37C669
30
DATA REGISTER (FIFO)
Address 3F5 READ/WRITE
All command parameter information, disk data
and result status are transferred between the
host processor and the floppy disk controller
through the Data Register.
Data transfers are governed by the RQM and
DIO bits in the Main Status Register.
The Data Register defaults to FIFO disabled
mode after any form of reset.
This maintains
PC/AT hardware compatibility.
The default
values can be changed through the Configure
command (enable full FIFO operation with
threshold control). The advantage of the FIFO
is that it allows the system a larger DMA latency
without causing a disk error.
Table 15 gives
several
examples
of
the
delays
with
a
FIFO.
The data is based upon the following
formula:
Threshold # x
1
-1.5 s = DELAY
DATA RATE
At the start of a command, the FIFO action is
always disabled and command parameters
must be sent based upon the RQM and DIO bit
settings. As the command execution phase is
entered, the FIFO is cleared of any data to
ensure that invalid data is not transferred.
An overrun or underrun will terminate the
current command and the transfer of data. Disk
writes will complete the current sector by
generating a 00 pattern and valid CRC. Reads
require the host to remove the remaining data
so that the result phase may be entered.
Table 13- FIFO Service Delay
FIFO THRESHOLD
EXAMPLES
MAXIMUM DELAY TO SERVICING
AT 2 Mbps* DATA RATE
1 byte
2 bytes
8 bytes
15 bytes
1 x 4 s - 1.5 s = 2.5 s
2 x 4 s - 1.5 s = 6.5 s
8 x 4 s - 1.5 s = 30.5 s
15 x 4 s - 1.5 s = 58.5 s
FIFO THRESHOLD
EXAMPLES
MAXIMUM DELAY TO SERVICING
AT 1 Mbps DATA RATE
1 byte
2 bytes
8 bytes
15 bytes
1 x 8 s - 1.5 s = 6.5 s
2 x 8 s - 1.5 s = 14.5 s
8 x 8 s - 1.5 s = 62.5 s
15 x 8 s - 1.5 s = 118.5 s
FIFO THRESHOLD
EXAMPLES
MAXIMUM DELAY TO SERVICING
AT 500 Kbps DATA RATE
1 byte
2 bytes
8 bytes
15 bytes
1 x 16 s - 1.5 s = 14.5 s
2 x 16 s - 1.5 s = 30.5 s
8 x 16 s - 1.5 s = 126.5 s
15 x 16 s - 1.5 s = 238.5 s
*The 2 Mbps data rate is only available if VCC = 5V.
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