AM8530H AMD [Advanced Micro Devices], AM8530H Datasheet - Page 176

• Manufacturer Part Number: AM8530H
• Description: Serial Communications Controller
• Manufacturer: AMD [Advanced Micro Devices]

SCC Application Notes
functionally distributed computers. Lengthy delays are often encountered in a centralized
system due to overloaded CPUs and slow communication lines.
f. Resource Sharing—
The advantages of distributed processing, therefore, point mainly to two important facts:
1. LANs make distributed intelligence practical.
2. Methods must be devised in order to allow large amount of data to be transported, at
This discussion addresses the second factor.
7.6.2
Today’s data communications market can be segmented in terms of speed.
i. Low speed (300 baud–56 kbaud)
ii. Medium speed (0.5 Mb/s–3 Mb/s)
iii. High speed (10 Mb/s–60 Mb/s)
iv. Very high speed (100 Mb/s and up)
On medium speed applications data rate is assumed at 1 Mb/s. At this rate, the physical
interface requires a highly sophisticated transceiver. The following is a list of the require-
ments:
a. The transceivers must have good but inexpensive isolation from the cabling system
b. The transceiver must be able to support a good collision avoidance scheme, since all
c. The receiver must be able to inhibit false starts due to noise in the surrounding
d. The transmitter must control the slew rate of the output signal to reduce EMI/RFI to
e. If an isolation transformer is used, some form of data encoding must also be
Why the Am7960
The Am7960 Coded Data Transceiver is designated to meet all the requirements of the
medium-speed network. It is frequency agile for data rates between 0.5 Mb/s to 3 Mb/s.
Electro–Magnetic Interference
The Am7960 has an external resistor connected from the slew rate control pin (TSRC) to
ground to control the transmit slew rate. If the rise and fall times of the output signal are
each 30% of the transmit clock period, the output waveform looks approximately like a
sine wave (Figure 7–17). This has a smoothing effect on the transmitted signal, reducing
3rd, 5th and higher order harmonics. This in turn reduces energy radiating from the cable
and minimizes the effects of electro-magnetic interference and radio frequency inter-
ference.
Remote sites in a distributed system can use each other’s facilities such as sharing
expensive peripheral devices in the system.
high speeds, between centers of intelligence.
(large common-mode voltages and surge voltages are common phenomenons in any
network). Pulse transformers can provide the required isolation.
devices have equal access to the network (in a CSMA type architecture). If a collision
does occur, the transceiver must detect the collision and flag the communications
controller.
environment.
surrounding electronic equipment. This is a very important criterion if the network is to
meet FCC/VDE regulations on radiation.
implemented so that a series of ‘1’s or ‘0’s do not saturate the transformer by
charging it to either voltage level.
Data Communications at the Physical Layer
AMD
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