Architectural Overview
1-8 Élan™SC520 Microcontroller User’s Manual
1.3.11 System Testing and Debugging Features (Chapter 24)
To facilitate debugging, the ÉlanSC520 microcontroller provides observability of many
portions of its internal operation, including:
■ A three-pin interface that can be used in either system test mode or write buffer test
mode, to aid in determining internal bus initiators of SDRAM cycles, and determining
when SDRAM data is valid on the interface. An additional mode provides observability
of integrated peripheral accesses.
■ A nonconcurrent arbitration mode to reduce debug complexity when PCI bus masters
and GP bus DMA initiators are also accessing SDRAM.
■ CPU cache control and dynamic core clock speed control under program control.
■ Ability to disable write posting and read prefetching in the SDRAM controller to simplify
tracing of SDRAM cycles.
■ Notification of memory write protection and non-executable memory region violations.
1.4 APPLICATIONS
The figures on the following pages show the ÉlanSC520 microcontroller as it might be used
in several reference design applications in the data communications, information
appliances, and telecommunication markets.
1.4.1 Smart Residential Gateway
Figure 1-2 on page 1-10 shows an ÉlanSC520 microcontroller-based Smart Resident
Gateway (SRG), which is a router for a home network between the wide area network
(WAN) (the internet) and a local area network (LAN) (an intranet of computers and
information appliances in the home). The SRG provides firewall protection of the LAN from
unauthorized access through the internet. A common internet access medium is shared by
all users on the LAN.
A variety of connections are possible for both the WAN and the LAN. For example, the
WAN connection can be a V.90 modem, cable modem, ISDN, ADSL, or Ethernet.
The LAN connection can be:
■ HomePNA—Home Phoneline Networking Alliance, an alliance with a widely endorsed
home networking specification
■ Bluetooth—a computing and telecommunications industry specification that describes
how computing devices can easily interconnect with each other and with home and
business phones and computers using a short-range wireless connection)
■ Home RF—a standard competing with Bluetooth for the interconnection of computing
devices in a LAN using radio frequency
■ Ethernet—local area network technology
■ Power line—a LAN using the AC power distribution network in a home or business to
interconnect devices. Digital information is transmitted on a high-frequency carrier signal
on top of the AC power.
1.4.2 Thin Client
Figure 1-3 on page 1-11 shows an ÉlanSC520 microcontroller-based “thin client,” which is
the modern replacement for the traditional terminal in a remote computing paradigm.
Application programs run remotely on a server, and data is warehoused on centrally
managed disks at the “server farm.” An efficient communications protocol transmits
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