T48C862M-R3 datasheet(14/107 Pages) ATMEL

14 / 107 page

T48C862-R3

4554A–4BMCU–02/03

Reset Function

During each reset (power-on or brown-out), the I/O configuration is deleted and

reloaded with the data from the configuration memory. This leads to a slightly different

behavior compared to the ROM versions. Both devices switch their I/Os to input during

reset but the ROM part has the mask selected pull-up or pull-down resistors active while

the MTP has them removed until the download is finished.

Microcontroller

Architecture General

Description

The microcontroller consists of an advanced stack-based, 4-bit CPU core and on-chip

peripherals. The CPU is based on the Harvard architecture with physically separated

program memory (ROM) and data memory (RAM). Three independent buses, the

instruction bus, the memory bus and the I/O bus, are used for parallel communication

between ROM, RAM and peripherals. This enhances program execution speed by

allowing both instruction prefetching, and a simultaneous communication to the on-chip

peripheral circuitry. The extremely powerful integrated interrupt controller with associ-

ated eight prioritized interrupt levels supports fast and efficient processing of hardware

events. The microcontroller is designed for the high-level programming language

qFORTH. The core includes both an expression and a return stack. This architecture

enables high-level language programming without any loss of efficiency or code density.

Figure 9. Microcontroller Core

Components of

Microcontroller Core

The core contains ROM, RAM, ALU, program counter, RAM address registers, instruc-

tion decoder and interrupt controller. The following sections describe each functional

block in more detail.

Program Memory

The program memory (EEPROM) is programmable with the customer application

program during the fabrication of the microcontroller. The EEPROM is addressed by a

12-bit wide program counter, thus predefining a maximum program bank size of

4-Kbytes. The lowest user program memory address segment is taken up by a

512 bytes Zero page which contains predefined start addresses for interrupt service rou-

tines and special subroutines accessible with single byte instructions (SCALL).

Instruction

decoder

CCR

TOS

ALU

RAM

Program

256 x 4-bit

MARC4 CORE

Clock

Reset

Sleep

Memory bus

I/O bus

Instruction

bus

Reset

System

clock

Interrupt

controller

On-chip peripheral modules

memory

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