AT90S/LS4434 and AT90S/LS8535

3

allows the program memory to be reprogrammed in-system

through an SPI serial interface or by a conventional nonvol-

atile memory programmer. By combining an 8-bit RISC

CPU with In-System Programmable Flash on a monolithic

chip, the Atmel AT90S4434/8535 is a powerful microcon-

troller that provides a highly flexible and cost effective solu-

tion to many embedded control applications.

The AT90S4434/8535 AVR is supported with a full suite of

program and system development tools including: C com-

pilers, macro assemblers, program debugger/simulators,

in-circuit emulators, and evaluation kits.

Comparison between AT90S4434 and AT90S8535

The AT90S4434 has 4K bytes of In-System Programmable

Flash, 256 bytes of EEPROM, and 256 bytes of internal

SRAM.

The AT90S8535 has 8K bytes of In-System Programmable

Flash, 512 bytes of EEPROM, and 512 bytes of internal

SRAM.

Table 1 summarizes the different memory sizes for the two

devices.

Pin Descriptions

VCC

Digital supply voltage

GND

Digital ground

Port A (PA7..PA0)

Port A is an 8-bit bi-directional I/O port. Port pins can pro-

vide internal pull-up resistors (selected for each bit). The

Port A output buffers can sink 20mA and can drive LED dis-

plays directly. When pins PA0 to PA7 are used as inputs

and are externally pulled low, they will source current if the

internal pull-up resistors are activated.

Port A also serves as the analog inputs to the A/D Con-

verter.

Port B (PB7..PB0)

Port B is an 8-bit bi-directional I/O pins with internal pull-up

resistors. The Port B output buffers can sink 20 mA. As

inputs, Port B pins that are externally pulled low will source

current if the pull-up resistors are activated.

Port B also serves the functions of various special features

of the AT90S4434/8535 as listed on page 52.

Port C (PC7..PC0)

Port C is an 8-bit bi-directional I/O port with internal pullup

resistors. The Port C output buffers can sink 20 mA. As

inputs, Port C pins that are externally pulled low will source

current if the pull-up resistors are activated. Two Port C

p i ns ca n a l t e r n a t i v el y b e use d as osci lla t o r fo r

Timer/Counter2.

Port D (PD7..PD0)

Port D is an 8-bit bidirectional I/O port with internal pull-up

resistors. The Port D output buffers can sink 20 mA. As

inputs, Port D pins that are externally pulled low will source

current if the pull-up resistors are activated.

Port D also serves the functions of various special features

of the AT90S4434/8535 as listed on page 59.

RESET

Reset input. A low on this pin for two machine cycles while

the oscillator is running resets the device.

XTAL1

Input to the inverting oscillator amplifier and input to the

internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier

AVCC

This is the supply voltage pin for the A/D Converter. It

should be externally connected to VCC via a low-pass filter.

See page 47 for details on operation of the ADC.

AREF

This is the analog reference input for the A/D Converter.

For ADC operations, a voltage in the range AGND to AV

CC

must be applied to this pin.

AGND

Analog ground. If the board has a separate analog ground

plane, this pin should be connected to this ground plane.

Otherwise, connect to GND.

Crystal Oscillators

XTAL1 and XTAL2 are input and output, respectively, of an

inverting amplifier which can be configured for use as an

on-chip oscillator, as shown in Figure 1. Either a quartz

crystal or a ceramic resonator may be used. To drive the

device from an external clock source, XTAL2 should be left

unconnected while XTAL1 is driven as shown in Figure 2.

For the Timer Oscillator pins, PC6(OSC1) and PC7(OSC2),

the crystal is connected directly between the pins. No

external capacitors are needed. The oscillator is optimized

for use with a 32,768 Hz watch crystal. An external clock

signal applied to this pin goes through the same amplifier

having a bandwidth of 256 kHz. The external clock signal

should therefore be in the interval 0 Hz - 256 kHz.

Table 1. Memory Size Summary

Part

Flash

EEPROM

SRAM

AT90S4434

4K bytes

256 bytes

256 bytes

AT90S8535

8K bytes

512 bytes

512 bytes