AVR-CDC-IO.pdf

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Virtual COM Port over Low-Speed USB

AVR-CDC

Home About CDC-232 CDC-IO CDC-SPI Driver Download FAQ Reference

About

CDC-IO

CDC-232

Usage

CDC-IO manipulates the AVR's Special Function Registers (SFR) through a virtual COM port on PC. It enables

reading/writing the MCU's parallel port freely. With the operations of Timer/Counter, PWM, A/D Converter, or

EEPROM, PC application achieves an advanced control over the device.

Schematics

CDC-IO

Usage

Schematics

Sample Program

CDC-SPI

Usage

Schematics

Sample Program

The External Interface using Software-USB

Driver

CDC Protocol

Usage

Windows

Mac OS

The installation is the same as CDC-232. The baudrate is arbitrary. Send text style commands from terminal software

or from your application on PC. If you need faster data transfer, Use "lowcdc.vbs" to switch to the bulk transfer mode.

Linux

CDC-IO Instruction Set

FAQ

Device Recognition

Function Command Format

Response

Who

@ @

"cdc-io", CR-LF

Communication Problem

Get

? address ?

data, CR-LF

Set

= data address =

CR-LF

Others

AND & Set

& data address & CR-LF

OR & Set

| data address |

CR-LF

Download

EX-OR & Set ^ data address ^

CR-LF

Set Double

$ data2 data1 address $ CR-LF

ATtiny2313 version has "Set","Get","Xor" only.

Reference

address: memory mapped SFR address in hex

data: 8 bit data in hex

delimiter: Tab, Space, CR, LF

predefined addr: (case-insensitive, NOT supported at ATtiny2313)

PINB, DDRB, PORTB PINC, DDRC, PORTC PIND, DDRD, PORTD

Example: ('_' means delimiter)

DDRB_?_ Replies DDRB value with CR-LF.

12_34_=_ Write 0x12 to address:0x34, replies CR-LF.

FB_PORTC_&_ Write (PORTC & 0xFB) to PORTC, replies CR-LF.

(ATtiny2313)

36_?_ Replies PINB(0x36) value with CR-LF.

12_37_=_ Write 0x12 to DDRB(0x37), replies CR-LF.

FB_38_^_ Write (PORTB ^ 0xFB) to PORTB(0x38), replies CR-LF.

Previous data and addr can be reused. Just enter command char to repeat.

"Set Double" command is used to write into EEPROM.

Avoid changing the port bits shared with USB signals. Use '&', '|' or '^' to modify the port direction. Use PIN* to toggle

bits if the port is assigned to output.

While enabling interrupt, the interrupt vector number is reported when invoked.

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Any SFRs are accessible. See AVR datasheet to use Timers, ADC, EEPROM, etc.

Schematic s

If the Vcc of the target circuit is 5V and the AVR's port is configured as input, insert some registers (3K3-10Kohms) to

prevent backward current.

Use crystal oscillator. Although ceramic resonator works well in most cases, it becomes unstable if the frequency

deviation is bigger.

ATtiny45/85 uses internal RC oscillator and PLL. It is calibrated to 16.5MHz by the USB signal when connected.

CDC-IO for ATtiny45-20

CDC-IO for ATtiny461-20

Only the "Set", "Get" and "Xor" commands are implemented in ATtiny2313's limited memory. This version has no

interrupt-report mechanism.

CDC-IO for ATtiny2313-20

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CDC-IO for ATmega8/48/88-20

Sample Program

These are the experimental circuit and the sample programs for ATmega8/48. These programs are written in C, VB,

VC, VC++, and C#. You can use any other languages (or macros) if they support RS-232C communication.

The volume control changes the buzzer tone and the LED's blinking pattern.

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