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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
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