■ The ROM/Flash memory interface provides the flex-
ibility to optimize the performance of ROM cycles,
including the support of burst-mode ROMs. This is
beneficial because products based on the
ÉlanSC400 and ÉlanSC410 microcontrollers may
be implemented such that the operating system or
application programs are executed from ROM.
tem performance by significantly reducing traffic on
the DRAM bus.
■ System management mode (SMM) facilitates de-
signs requiring power management by providing a
mechanism to control power to unneeded peripher-
als transparently to application software.
To reduce power consumption, the floating-point unit
has been removed from the Am486 CPU core. Float-
ing-point instructions are not supported on the
ÉlanSC400 and ÉlanSC410 microcontrollers, although
normal software emulation can be easily implemented.
■ Because the microcontrollers support a large num-
ber of external buses and interfaces, the address
and data buses are shared between the various in-
terfaces to reduce pin count on the chip.
These features result in a versatile architecture that
can use various combinations of data bus sizes to
achieve cost and performance goals. The architecture
provides maximum performance and flexibility for high-
end vertical applications, but contains functionality for
a wider horizontal market that may demand less
performance.
The ÉlanSC400 and ÉlanSC410 microcontrollers use
the industry-standard 486 instruction set. Software
written for the 486 microprocessor and previous mem-
bers of the x86 architecture family can run on the
ÉlanSC400 and ÉlanSC410 microcontrollers.
Power Management
■ A typical lower performance/lower cost system
might implement 16-bit DRAM banks, an 8-bit ISA
bus, an 8/16-bit PC Card bus, and use the internal
graphic controller.
Power management on the ÉlanSC400 and
ÉlanSC410 microcontrollers includes a dedicated
power management unit and additional power man-
agement features built into each integrated peripheral.
The ÉlanSC400 and ÉlanSC410 microcontrollers can
use the following techniques to conserve power:
■ A higher performance, full-featured system might
include 32-bit DRAM, VL-bus to an external graph-
ics controller, and a 16-bit ISA/PC Card bus.
■ Slow down clocks when the system is not in active use
■ Shut off clocks to parts of the chip that are idle
■ Switch off power to parts of the system that are idle
■ Automatically reduce power use when batteries are low
The following basic data bus configuration rules apply.
(A complete list of feature trade-offs to be considered
in system design can be found in “System Consider-
ations” on page 20.)
The power management unit (PMU) controls stopping
and changing clocks, SMI generation, timers, activities,
and battery-level monitoring. It provides:
■ When the internal graphics controller on the
ÉlanSC400 microcontroller is enabled, DRAM is al-
ways 16 bits wide, and no 32-bit targets are sup-
ported. This is because the graphics controller
needs a guaranteed short latency for adequate
video performance. If either 32-bit DRAMs, 32-bit
ROMs, or the VL-bus is enabled, the internal graph-
ics controller is unavailable.
■ Hyper-Speed, High-Speed, Low-Speed, Temporary
Low-Speed, Standby, Suspend, and Critical
Suspend modes
■ Dynamically adjusted clock speeds for power
reduction
Note that, as a derivative of the original ÉlanSC400 mi-
crocontroller, the ÉlanSC410 microcontroller shares
the primary architectural characteristics of the
ÉlanSC400 microcontroller described above, minus
the graphics controller and PCMCIA interfaces.
■ Programmable activity and wake-up monitoring
■ General-purpose I/O signals to control external
devices and external power management
■ Battery low and AC power monitoring
■ SMI/NMI synchronization and generation
The following sections provide an overview of the fea-
tures of the ÉlanSC400 and ÉlanSC410 microcontrollers,
including on-chip peripherals and system interfaces.
Clock Generation
The ÉlanSC400 and ÉlanSC410 microcontrollers re-
quire only one 32.768-kHz crystal to generate all the
other clock frequencies required by the system. The
output of the on-chip crystal oscillator circuit is used to
generate the various frequencies by utilizing four
Phase-Locked Loop (PLL) circuits (three for the
ÉlanSC410 microcontroller). An additional PLL in the
CPU is used for Hyper-Speed mode.
Low-Voltage Am486 CPU Core
The ÉlanSC400 and ÉlanSC410 microcontrollers are
based on the low-voltage Am486 CPU core. The core
includes the following features:
■ 2.7–3.3-V operation reduces power consumption
■ Industry-standard 8-Kbyte unified code and data
write-back cache improves both CPU and total sys-
14
Élan™SC400 and ÉlanSC410 Microcontrollers Data Sheet
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