Atmel AVR128 Installation and operating instructions

AVR 8-bit Microcontrollers

AVR128: Setup and Use of the AVR Analog

Comparator

APPLICATION NOTE

Introduction

This application note serves as an example on how to set up and use the

Atmel® AVR® On-chip Analog Comparator. The following program examples

are given in the assembly file “avr200.asm”:

•Detect a positive edge on the comparator output by polling the ACO-

bit in the Analog Comparator Control and Status Register – ACSR.

•Detect a positive edge on the comparator output by polling the Analog

Comparator Interrupt Flag – ACI in ACSR.

•Initialize interrupt on comparator output toggle. An interrupt routine

which increments a 16-bit counter each time it is executed is given as

an example.

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

Table of Contents

Introduction......................................................................................................................1

1. Detecting a Positive Edge By Polling ACO................................................................3

2. Detecting a Positive Edge by Polling ACI.................................................................. 4

3. Using the Analog Comparator Interrupt..................................................................... 6

4. Revision History.........................................................................................................7

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

1. Detecting a Positive Edge By Polling ACO

This part of the code shows the trivial way of detecting a positive edge on the comparator output. Even

though it uses only four words of code and no initial setup, this approach to the task might cause

problems. If a short pulse on the output occurs while the program is administrating the wait loop, the

pulse could be missed as ACO is directly connected to the comparator output. If the user wants to insert

code within the wait loop, the probability of detecting a short pulse will increase. Such code might be time-

out if no edge occurs within a specific period. The procedure for detection is as follows:

1. If output is high, wait for output to go low.

2. Wait until output goes high.

Figure 1-1. ACO Polling Flow Chart

S TART

DONE

ACO = 0?

ACO = 1?

Table 1-1. ACO Polling Performance Figures

Parameter Value

Code Size (Words) 4

Response Time (Cycles) 3 - 5

Initialization Time (Cycles) 0

High Registers: None

Pointers: None

Interrupts Usage None

Peripherals Usage Analog Comparator

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

2. Detecting a Positive Edge by Polling ACI

This part of the code shows a far more secure and flexible way of detecting a positive edge on the

comparator output. Even though the Analog Comparator Interrupt is disabled, the interrupt flag will still be

set when events on the comparator output matches the settings of the ACIS1/ACIS0 bits in ACSR. E.g., a

positive edge will always set the ACI bit in ACSR if ACIS1/ACIS0 both are one (refer to the datasheet for

details). The ACI flag will reflect whether the event to look for has occurred since the last ACI Reset. In

this application note, positive edge detection by polling ACI is implemented according to the following

procedure:

Setup

1. Set ACIS0 and ACIS1 = 1.

Polling

1. Clear the ACI bit by writing a logical "1" to it.

2. Wait until ACI goes high.

Figure 2-1. ACI Polling Flow Chart

S ETUP

DONE

ACO = 1?

ACIS 1/ACIS 0 ← 11

CLEAR ACI

Table 2-1. ACI Polling Performance Figures

Parameter Value

Code Size (Words) 5

Initialization Time (Cycles) 2

Response Time (Cycles) 3 - 5

High Registers: None

Pointers: None

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

Parameter Value

Interrupts Usage None

Peripherals Usage Analog Comparator

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

3. Using the Analog Comparator Interrupt

The application note program shows an example on how to enable the comparator interrupt. In the

example, interrupt on comparator toggle is shown. The following procedure is followed:

1. Clear interrupt flag and ACIS1/ACIS0. The interrupt flag must be cleared first. If not, and the flag for

some reason already is set, the MCU will start executing the interrupt routine immediately when the

interrupts is enabled. Clearing ACIS1/ACIS0 selects interrupt on toggle.

2. Enable Global Interrupts.

3. Enable the Analog Comparator Interrupt by setting the ACIE bit in ACSR.

Note that since the ACSR Register is one of the lower 32 I/O, registers, the “SBI” instruction can be used

to set, clear and test bits.

Table 3-1. Analog Comparator Interrupt Enable Performance Figures

Parameter Value

Code Size (Words) 4

Execution Time (Cycles) 5

High Registers: 1

Pointers: None

Interrupts Usage None

Peripherals Usage Analog Comparator

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

4. Revision History

Doc. Rev. Date Comments

0934C 07/2016 New template

0934B 05/2002

0934A Initial document release.

Atmel AVR128: Setup and Use of the AVR Analog Comparator [APPLICATION NOTE]

Atmel-0934C-Setup-and-Use-of-the-AVR-Analog-Comparator_AVR128_Application Note-07/2016

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