which mcu is suitable???

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i would like to find mcu with following requirements:

_ USB Device full speed
_ SPI (Master)
_ RTC with 38Khz quartz
_ 16K Bytes of Flash
_ 512 Bytes of RAM

i would like to use the AVR Atmega16U4, however i find that this MCU has no RTC (for Date/Time in sleep mode).

anyone can help??

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Could you use an external RTC instead?

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my first reaction:

what does the atmel parametric table say on such a device ????

I know there is derivative of the mega128 that has 1 usb port and a uart port in stead of 2 uart ports. It supports SPI I think has rtc capabilities and ahs more then enough FLASH and RAM.

perhaps check if this derivative is also available in smaller versions.

regards

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Here is a link to the table (it's a little hard to find):
[url]
http://www.atmel.com/dyn/product...
[/url]

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An AT90USB64 should fit the bill.

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my question is if AVR mcu comes with RTC (real time clock) with 38Khz quartz...

since it should different from RTC (Real time counter)... right???

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Quote:
my question is if AVR mcu comes with RTC (real time clock) with 38Khz quartz...

None have a RTC per se, but many AVRs have the ability to connect a crystal directly to a timer (usually it is a 32.678kHz crystal though). With the addition of a small amount of software, that can be used as an RTC. The AT90USB64 that jayjay mentioned is one of those (search for TOCS in the datasheet)>

Regards,
Steve A.

The Board helps those that help themselves.

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Also check out the XMega series. It has a "High Precision" 32 KHz internal clock, which might meet your needs.

JC

AVR XMega System Clock and Clock Options, (Section 7):

Quote:
• Fast start-up time
• Safe run-time clock switching
• Internal Oscillators:
– 32 MHz run-time calibrated RC oscillator
– 2 MHz run-time calibrated RC oscillator
– 32.768 kHz calibrated RC oscillator
– 32 kHz Ultra Low Power (ULP) oscillator with 1 kHz output
• External clock options
– 0.4 - 16 MHz Crystal Oscillator
– 32 kHz Crystal Oscillator
– External clock
• PLL with internal and external clock options with 1 to 31x multiplication
• Clock Prescalers with 1 to 2048x division
• Fast peripheral clock running at 2 and 4 times the CPU clock speed
• Automatic Run-Time Calibration of internal oscillators
• Crystal Oscillator failure detection

Edit: Changed Internal Xtal to Internal Clock...

Last Edited: Tue. Nov 10, 2009 - 04:59 PM
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Note that the AVR's RTC only operates while the chip has power, and cannot be kept "alive" with a battery backup easily. If you require date & time to be maintained for extended periods without external power applied, use an external RTC chip that interfaces to your AVR over I2C or SPI. [yes the AVR's sleep modes can be used, but you will consume more power than the external RTC with the AVR, and the battery will need to power the rest of your circuit, or you will otherwise need complex circuitry to isolate the AVR from the rest of the circuit during powered off times. End result is that it'll be cheaper/faster to use the external RTC which is designed for this pupose]

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Quote:

32 KHz internal xtal

I'm always intrigued by these "internal crystals". Exactly where in that piece of plastic/silicon does the quartz actually live then?

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:twisted: I'm afraid those internal crystals are not alive. It's their spirit reincarnated in the form of an RC oscilator, probably trimmed, much worse in precission. But that's why phantoms are semitransparent, huh?

SAM3U has some nice and similar features, including an external power pin to power only few internal registers and a really low power oscilator for the 32KHz (and some nice wake up circuitry), but I think this is out of scope?

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Why couldn't they stuff a crystal inside a chip? They can make SMD crystal oscillators that are 3.2x5.0mm.

A RTC is a very simple device of course and with modern technology the die is so small you likely cannot even see it with the naked eye; so plenty of space inside a DIP or SO8 :)