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Hi all kindly help me. I'm looking for possible MCU to use, basic requirements would be: 1. on-chip RTC or mcu that can generate accurate time for RTC 2. LCD of around 100 segments, on-chip driver, or software driver 3.SPI,I2C and UART on-chip 4. ARound 32k flash, 1-2k RAM 5. GPIO of aorun 30pins for LCD if software, 1set of SPI,1set of I2C, UART, and 5 extra pins 6. LOW COST
Possible cortex m0,m3 or 8051 family. Help really appreciated
Thank you
What is "accurate time"?
A chip that supports a 32768Hz crystal will produce more accurate time than a chip that makes use of the processor crystal to drive a hw or sw RTC.
The processor crystal isn't produced with as good tolerances. And working at higher frequencies means that it is a smaller and lighter quartz so diffusion of foreign atoms that got stuck inside the casing will result in a larger drift from ageing than with the large and slow 32768Hz crystals.
http://www.keil.com/dd/search_parm.asp ?
i did have problem on how to explain that. i found some IC that has dual crystal, one has 32768Hz input, but it didnt say its for RTC. so i was thinking that maybe there some IC of same characteristic so i use term accurate, and that it generate interrupt to create a its RTC. soo my accurate term should be exact as like 2% per month accuracy base on RTC datasheet. upon my search found this: www.holtek.com/.../56R67_668_678.htm
but im more interested on using cortex-m0. also on ST cortexM3, found it on mouser around $3+ which should work + there LCD library, and nxp cortexm0 $.65 but low pin count and I think ill be having problem on generating LCD for my 100segments
so is there some cortex IC or 8051 that fit my requirement?
also, can i log-in on keil forum? as i always enter my email,name....to post?
thank you Per Westermark
I did tried that, but basically cost come on my way. as also i have this in mind, IC from US is costly but on quality its really reliable.
nuvoton would be a good way to start, but all there m0 are still on sample stage. also they have this development tools for $29 O.O
forgot to add: power down mode as it will be battery powered and low power MCU
An accuracy of 2% per month means that it will drift 1 second every 50 seconds.
An accuracy of 2 seconds per month is very, very, very hard to manage unless you buy/design a crystal oscillator with oven to keep the crystal at a constant temperature.
An internal RTC requires an oscillator. This may be the main crystal. Or a dedicated watch crystal (better tolerances and also allows the RTC to continue to operate when the processor is in low-power mode with main oscillator stopped). Or an external oscillator that just feeds the correct frequency to the RTC.
I don't have much experience with chips that have specific driving support for LCD so I'll stay away from discussing specific chips.
The tolerances depends on the oscillator design, and not on the internal logic of the RTC. Some RTC have logic where you can program a drift correction (i.e. a number of seconds to add/remove each month) but that isn't too easy to use. And it also requires that the oscillator has a known behaviour or that you have access to a reference clock somewhere to measure drift.
Thank you for brief explanation. to lower my requirements, I just need Micro that has RTC,LCD(100segments=4*25=29GPIO),sleep mode and low cost.base on my search i think no cortex that has it. if you've click that holtek site, that would be my perfect choice, but some consideration needed, as like reliable tools and more...
thank you