determining microcontroller speed & memory size

[squadra]

I am building a remote controlled pre amp.
Functionality is limited to selecting one of the four inputs and selecting the required attenuation.
Selecting the correct input is done via relais, and volume selection via relais (TVC) or PGA2311 (will test both).
The relais will be controlled via serial/parallel converters.

Because of it's low price I have ordered the AVR ISP and downloaded the AVR studio software; it will be an AVR microcontroller
The AVR attiny 26 is cheap, which makes it a good candidate
It has been very long since I have worked with microcontrollers and assembly and I am wondering how to determine the clock speed for the RC5 receiver.
The AVR has an internal clock of 1MHz, this is probably fast enough for decoding RC5?

Memory size is not important, I only need a few bytes for the actual channel & volume settings.

Also I have no idea what flash size is necessary, are there guidelines for this?

 

[Wynand]

Did you get the low voltage version ATTiny26 or ATTiny26L

 

[Wynand]

It doesn't really matter, but why not use a crytal, we made a remote control for a pc, using a atmega32 and a 6Mhz crystal.

It adds frexibility to the design (and accuracy).
You can alway use the prescaler to get a slower freq.

 

[squadra]

Did you get the low voltage version ATTiny26 or ATTiny26L

It is the ATTiny26, max. 16MHz version.

On a webpage I found the speed of RC5 is only about 560Hz (1.8ms per bit).
I thought it was 36kHz, but that is just the carrier.

 

[Pyramid]

squadra- Regarding your question about xtal selection: If you are going to use the serial port for input, then you might want to pick a xtal that will give you an exact (or close) baud rate of 560. If you are going to decode by looking at an edge to start and use software delays to sample (or oversample for best noise rejection) the input stream, then just about any xtal will give the the needed resolution at the RC5 baud rate. When considering xtal selection, I always consider all peripherals attached to the micro, timing and delay requirements, tone generation accuracy and resolution, number of interupts and service speed or anything else that might create a timing issue. Rarely can you find a xtal that will meet all of the requirements exactly, but compromises can be made and a choice can be determined that should meet all your criteria.

Flash size is less of an issue today than it was years ago when devices were very limited to 2K (8749) or 4K (8751). Choice of programming language may make a difference, in my experience, assembly language requires far less space than C. You will want to leave a comfortable (apply your definition here) buffer of extra code space in case you want to make changes or add capabilities in the future. I do not know of any formula or equation that would apply to flash size. Usually, more is better, balanced with cost and pin count needed to get it.