Mega88_&_ATA6824_High_temperature_H-Bridge_system Documentation

Description

This software package has been developped to run on the board described in the application note attached to it.
It makes a short demonstration of ATmega88 and ATA6824 capabilities.
It embeddes a complete H-bridge system able to run a DC motor with one or two hall sensors in high temperature
conditions (up to 150°C ambiant).

The main source files are :

• main.c
  main loop, manages ADC acquisitions, time base, watchdog refresh, motor operation, fault display and clear
• ADC_task.c
  ADC is used to acquire Motor current, desired speed and Vbat
• an_compare.c
  Analog comarator allows to detect over current conditions by generating an interrupt
• ATA6824_defs.c
  ATA6824 routines (Watchdog refresh, diagnostic, diagnotic interrupts)
• Hall_sensors.c
  Manages optionnal hall sensor(s) pin change interrupts
• Timer0_PWM.c
  Timer0 used to generate PWM and Software time base

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Functionnalties

This demonstration software allows to operate a DC motor through on-board switch and potentiometer

• Motor can be operated clockwise/counter-clockwise with speed variation.
  
• Diagnostics are provided thanks to ATA6824 driver capabilities.
  Short-cirtcuits, voltage and temperature monitoring are implemented through it.
  Output PWM is switched of in case of either a short-circuit or an over-current is detected.
  
• No motor command strategy has been implemented, as it depends on the final
  application requirements. However, some caution should be taken. Indeed, an
  accelerating curve for the motor would be welcome to avoid bad short-circuit
  detection at motor startup for example.
• This application comes as a standalone System. Implementing serial link
  would allow to integrate it in a network structure, with remote controls.

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Main Peripheral Use

Peripherals managed by this software:

• Timer 0 generates PWM through output compare and Software time base
• Pin Change interrupts 10, 11 & 12 for ATA6824 diagnostic pins, 6 & 7 for hall sensors
• ADC is used for Motor current, desired speed and Vbat measurements
• Analog comarator generates overcurrent interrupts
• External ATA6824's watchdog

Peripherals not managed by this software (but on-board hardware is implemented)

• Uart can be used to transmit/receive data using SIO (ATA6824's high voltage serial interface)

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ATmega88 Fuses configuration

• 8Mhz internal RC Oscillator in being used

Caution about MCU start-up time in Fuse configuration :

• Care should be taken in Fuse configuration to set up a MCU start-up time of 0ms or 4.1ms. (By default, it is set to 65ms)
• ATA6824 waits a watchdog trigger before typically td = 68ms with 10% tolerance
• When no trigger happens during this period of time, MCU is reseted.
• Default MCU startup time is set to 65ms, which might be too long regarding td (68ms ~10%) before a reset occur.
  MCU won't be able to generate the WD trig if td < 65ms. As a result, MCU won't start before being reseted!

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Software compilation & Tools

It can be compiled either using IAR EWAVR4.20A or avr-gcc (WinAVR-20060421 with AVR Studio 4.12 Service pack 4, both free of charge).

• To use it under IAR, open the ewp project file. The project should contain the previous described source files. You can compile it and open the compiled files under AVR Studio for MCU programming/debugging.
• To use it under avr-gcc, launch AVR Studio, create a new AVR-GCC project. In project configuration options, select the corresponding MCU (atmega88), add the project parent directory as an include directory and add the files described above. You can compile it and then make MCU programming/debugging.

The ATmega88 is supported by AVR Studio, version 4.12 or higher. For up-to-date information on this and other AVR tool products, please consult our web site. The newest version of AVR Studio, AVR tools and this user guide can be found in the AVR section of the Atmel web site, http://www.atmel.com

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