參數(shù)資料
型號(hào)： NS32FX100VF
廠商： National Semiconductor Corporation
英文描述： System Controller
中文描述： 系統(tǒng)控制器
文件頁(yè)數(shù)： 13/94頁(yè)
文件大?。?/td> 955K
代理商： NS32FX100VF
2.0 Architecture
(Continued)
After reset, RFRT is initialized to 6.
Writing to RFRT must be followed by read back
to ensure that the RFRT has, in fact, been up-
dated. This procedure must be repeated until
RFRT is updated (value read
e
value written).
RFRT exists only in the NS32FV100 and the
NS32FX200.
RFEN:
Refresh enable
7
6
5
0
res
EN
res
EN
0: No refresh transactions.
1: Refresh transactions are issued by
the chip according to the refresh
rate, selected by RFRT.
After reset EN is set to ‘‘1’’.
RFEN exists only in the NS32FV100 and the
NS32FX200.
2.2.3.1 Usage Recommendations
The ECOUNT bit, in MCFG, must be set to enable TCU
counters operation.
2.3 SIGMA-DELTA CODEC (SDC)
2.3.1 Features
#
16-bit format Analog-to-Digital converter and Digital-to-
Analog converter
#
Full and Half Duplex operation
#
Optimized for FAX and DATA Modems
#
Various sampling rates for voice and data applications
#
Total harmonic distortion better than
b
70 dB
#
Programmable IIR filters
D Programmable transmit filters
D Programmable receive filters
D Programmable echo canceling filter
#
Programmable gain control
#
Programmable fine timing tuning
#
Digital loop-back mode
#
Reduced CPU load by 12-level transmission FIFO and 12-
level reception FIFO
2.3.2 Operation
The Sigma Delta CODEC performs high resolution analog-
to-digital (A/D) and digital-to-analog (D/A) conversions us-
ing an over sampling technique. This module is optimized
for use as the analog front end for Digital Signal Processing
(DSP) applications such as modems or voice processing.
The SDC’s main advantage, compared to other A/D and
D/A convertors, is the use of digital circuitry resulting in high
reliability and reduced cost. The SDC solution incorporates
a second-order, digital Sigma-Delta modulator and a noise
shaping technique to improve performance.
The digital parts of the converters are implemented on-chip
and a few external components implement the analog parts.
NSFAX Software package fully supports the SDC. Software
drivers handle both the SDC initialization and data transfers.
National Semiconductor’s modem software is usually pro-
vided in binary form, and hence the internal structure of the
SDC is transparent to the user. A detailed description of the
SDC is available only for source-level customers.
2.3.2.1 Block Diagram
The Sigma-Delta CODEC block diagram is shown in Figure
2-4.
13
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