ELANSC310 datasheet(84/119 Pages) AMD

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Élan™SC310 Microcontroller Data Sheet

PREL IMINARY

VOLTAGE PARTITIONING

The ÉlanSC310 microcontroller supports both 3.3-V

system designs and mixed 3.3-V and 5-V system de-

signs. For 3.3-V-only operation, all supply pins (VCC,

VCC1, VCC5, VMEM, VSYS, VSYS2, and AVCC)

should be connected to the 3.3-V DC supply. To oper-

ate an interface at 5 V, the VCCIO pins associated with

that I/O interface should be connected to 5 V. All supply

pins of the same name should be connected to the

same voltage plane. The different supply pins and their

functions are described in this section.

Refer to the Pin Characteristics section beginning on

page 21 of this data sheet for the internal VCC rail

(VCCIO and VCC Clamp) to which each pin is electri-

cally attached.

For more details about the information in this section,

see the commercial and industrial operating voltage

ranges beginning on page 70. Also see Table 45 on

page 88 and its corresponding notes.

“Typical Power Numbers” on page 72 details the power

consumption of each of these supply pins in Maximum

ISA mode.

VCC — These supply pins are used to provide power

to the ÉlanSC310 microcontroller core only. They

should always be connected to a 3.3-V source.

VCC1 — This supply pin provides power to a subset of

the power management and ISA interface pins. It can

be connected to either a 3.3-V or 5-V source, depend-

ing on the logic threshold requirements of the external

peripherals attached to these interfaces. When con-

nected to the 5-V supply, all outputs with VCC1 as their

VCCIO will be 5 V. If connected to 3.3 V, all of these

outputs will be 3.3 V.

VCC5 — These supply pins are used to provide a 5-V

source for the 5-V input and output pins. If the system

design requires that the ÉlanSC310 microcontroller

support 5-V tolerant inputs, then this pin should be con-

nected to a 5-V DC source. This supply pin is the

VCCIO for the Parallel Port and Serial Port interfaces.

VMEM — This supply pin controls the operating volt-

age of the memory interface. When connected to the

5-V supply, all outputs to the main memory will be 5 V.

This includes the ÉlanSC310 microcontroller data bus.

Therefore, translation buffers may be required when in-

terfacing to 5-V devices on the data bus when the

memory interface is operating at 3.3 V.

VSYS — These supply pins provide power to a subset

of the ISA address and command signal pins, external

memory chip selects, buffer direction controls, and

other miscellaneous functions. They can be required to

operate at 3.3 V or 5 V, depending on the system de-

sign.

VSYS2 — This voltage pin should be connected to ei-

ther 3.3 V or 5 V, depending on the type of bus option

selected, the voltage threshold requirements of at-

tached devices, and the state of the other voltage pins

associated with the alternate function interface pins

(i.e., VCC1 and VSYS).

AVCC — This supply pin provides power to the analog

section of the ÉlanSC310 microcontroller. It should al-

ways be connected to a low-noise 3.3-V supply.

For more information, see the DC characteristics be-

ginning on page 70.

CRYSTAL SPECIFICATIONS

The ÉlanSC310 microcontroller on-chip oscillator is the

primary clock source driving all of the on-chip PLL

clock generators and the real-time clock (RTC) function

directly.

For problems with crystal startup, check that the spec-

ifications listed in this section are met, and refer to the

Troubleshooting Guide for Micro Power Off Mode on

ÉlanTMSC300 and ÉlanSC310 Microcontrollers and

Evaluation Boards Application Note, order #21810.

Externally, a parallel resonant PC/AT cut crystal

(32.768 kHz), two capacitors, and two resistors are re-

quired for the oscillator to function properly. It is critical

that the frequency of the oscillator circuit be as close as

possible to the nominal 32.768-kHz frequency for RTC

accuracy. By selecting the appropriate external circuit

components, this oscillator circuit can be made to op-

erate at very close to the nominal 32.768 kHz.

Figure 29 shows the complete oscillator circuit, includ-

ing the discrete component model for the crystal. In this

figure, the external discrete components that must be

supplied by the system designer are R

F, RB, CD, CG,

and XTAL. R

F is the external feedback resistor for the

on-chip amplifier. R

B provides some isolation between

the parasitic capacitance of the chip and the crystal.

The value of this resistor also has a very small effect on

the operating frequency of the circuit. C

D and CG are

the external load capacitors. The value of these capac-

itors, in conjunction with the other capacitive values

discussed below, have the most affect on the operating

frequency of this circuit.

The discrete components inside the dotted line repre-

sent the circuit model for the crystal, with C

O represent-

ing the crystal lead shunt capacitance. The dashed line

component C

STRAY represents the stray capacitance of

the printed circuit board. Typically, a crystal manufac-

turer provides values for all of the equivalent circuit

model components for a given crystal (i.e., L

1, C1, R1,

and C

O). In addition to these parameters, the manufac-

turer will provide a load capacitance specification usu-

a lly d e signa te d a s C

L . Th e lo ad c a p a c i t an c e

specification is the capacitive load at which the manu-

facturer has tuned the crystal for the specified

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