The AVR core combines a rich instruction set with 32 general-purpose working regis-
ters. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU),
allowing two independent registers to be accessed in one single instruction executed in
one clock cycle. The resulting architecture is more code efficient while achieving
throughputs up to ten times faster than conventional CISC microcontrollers.
The AT90S8535 provides the following features: 8K bytes of In-System Programmable
Flash, 512 bytes EEPROM, 512 bytes SRAM, 32 general-purpose I/O lines, 32 general-
purpose working registers, Real-time Clock (RTC), three flexible timer/counters with
compare modes, internal and external interrupts, a programmable serial UART, 8-chan-
nel, 10-bit ADC, programmable Watchdog Timer with internal oscillator, an SPI serial
port and three software-selectable power-saving modes. The Idle Mode stops the CPU
while allowing the SRAM, timer/counters, SPI port and interrupt system to continue
functioning. The Power-down mode saves the register contents but freezes the oscilla-
tor, disabling all other chip functions until the next interrupt or hardware reset. In Power
Save Mode, the timer oscillator continues to run, allowing the user to maintain a timer
base while the rest of the device is sleeping.
The device is manufactured using Atmel’s high-density nonvolatile memory technology.
The On-chip ISP Flash allows the program memory to be reprogrammed in-system
through an SPI serial interface or by a conventional nonvolatile memory programmer.
By combining an 8-bit RISC CPU with In-System Programmable Flash on a monolithic
chip, the Atmel AT90S8535 is a powerful microcontroller that provides a highly flexible
and cost effective solution to many embedded control applications.
The AT90S8535 AVR is supported with a full suite of program and system development
tools including: C compilers, macro assemblers, program debugger/simulators, in-circuit
emulators and evaluation kits.
Digital supply voltage.
Port A (PA7..PA0)
Port A is an 8-bit bi-directional I/O port. Port pins can provide internal pull-up resistors
(selected for each bit). The Port A output buffers can sink 20 mA 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 Converter.
The Port A pins are tri-stated when a reset condition becomes active, even if the clock is
Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port 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 AT90S8535 as listed on page 78.
The Port B pins are tri-stated when a reset condition becomes active, even if the clock is
Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output
buffers can sink 20 mA. As inputs, Port C pins that are externally pulled low will source