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MCUs (ATTiny)
This section added by Daveb who is looking for more info... see ATMEL's AVR and AVR32 - Quick Reference Guide for useful info.
ATTiny rather than an ATMEGA as it is smaller and lots cheaper or would use an arduino or similar. ATTiny rather than other MCUs for good free tool (GCC etc) support.
Doing searches on Farnell reveals lots of choices, with big price breaks (~40%) for 10 and (~20%) for 100. Price seems to roughly scale with pin count or maybe chip size.. but there are anomalies. It is worth picking a chip and buying a few. But how to choose the chip??
Points that matter to me..
- enough RAM for interrupt vectors, global state variables, C stack, local variables and interrupt stack
- excess code space for diagnostic code
Prototyping
- a few excess pins to allow for in-crcuit reprogramming and debugging (which i think means dont use MOSI,MISO,SCLK or RESET in the application)
An 8 pin dip has 2 pins available to the app (4 debug plus vcc and gnd), while a 14 pin dip has 8 app pins? Four times the app space for under 2x the size:)
in the farnell catalogue at moment i see some standouts.. These are all 8kflash, 512byte ram parts.
- Not in stock - ATTiny84A-PU 14 DIP, 1.8 to 5.5v, at upto 20Mhz, ADC with 1x, 20x prescale, £1.90(units), 1.39(10s), 1.28(100s)
- ATTiny 85-20PU 8 DIP, 2.7 to 5.5v, at upto 20 Mhz, £2.36(units), 1.36(10s), 1.14(100s)
- ATTiny861A-PU 20 DIP, 1.8 to 5.5v, upto 20Mhz, 3PWM, ADC with 1x, 8x, 20x and 32x prescaler :) £2.10, 1.72, 1.48
I like this prescaler, can see it simplifiying some designs.
The part that started my investigation - only 1k flash and 64bytes of ram - one 8 bit counter and no prescaler for the ADC.
- ATTiny13 8 pin DIP 2.7 to 5.5v, upto 20Mhz, £2.48(units), 1.55(10s), 1.13(100s)
- attiny13a 8 pin dip new version, 1.8v to 5.5v, upto 20Mhz, £2.48, 1.38(10s), 1.31(100s)
--- In stock now :)
- 1x attiny85-10pu 1.8v to 5.5v, 10MHz (after I took 1)
- 1x attiny13-20pu