Hello All, any suggestions for small (e.g. TSSOP20) microcontrollers with a good on-chip oscillator? One of the best I found is the 9S08 with 1% max. drift in the 0..70�C range. The 9S08 would do the job but is at it's speed limit. I don't want to tolerate much more frequency deviation to keep a certain margin for the fast async serial communication. 5V operation and a decent A/D-Converter would be great. TIA, Oliver -- Oliver Betz, Munich despammed.com is broken, use Reply-To:
Small controller with good on-chip oscillator
Started by ●February 21, 2013
Reply by ●February 21, 20132013-02-21
Oliver Betz <obetz@despammed.com> writes:> I don't want to tolerate much more frequency deviation to keep a > certain margin for the fast async serial communication.I thought for async you could be pretty sloppy, since the receiver is edge triggered by the start bit, and you just have to sample from somewhere in the interior of each of the 8 bits going by. So the timing could be off by hmm, well, several percent at least.
Reply by ●February 21, 20132013-02-21
Paul Rubin wrote:>> I don't want to tolerate much more frequency deviation to keep a >> certain margin for the fast async serial communication. > >I thought for async you could be pretty sloppy, since the receiver is >edge triggered by the start bit, and you just have to sample from >somewhere in the interior of each of the 8 bits going by. So the timing >could be off by hmm, well, several percent at least.Correct. On each side 1% temperature drift plus initial calibration tolerance plus aging plus slope and threshold asymmetry adds up quickly. Oliver -- Oliver Betz, Munich http://oliverbetz.de/
Reply by ●February 21, 20132013-02-21
On Thu, 21 Feb 2013 20:29:56 +0100, Oliver Betz <OBetz@despammed.com> wrote:>Paul Rubin wrote: > >>> I don't want to tolerate much more frequency deviation to keep a >>> certain margin for the fast async serial communication. >> >>I thought for async you could be pretty sloppy, since the receiver is >>edge triggered by the start bit, and you just have to sample from >>somewhere in the interior of each of the 8 bits going by. So the timing >>could be off by hmm, well, several percent at least. > >Correct. On each side 1% temperature drift plus initial calibration >tolerance plus aging plus slope and threshold asymmetry adds up >quickly.Or, if you have a spare timer capture pin, you could track the pulse widths and make the baud rate adaptable. Would not be appropriate for every situation, of course.
Reply by ●February 21, 20132013-02-21
On Thu, 21 Feb 2013 10:41:48 -0800, Paul Rubin wrote:> Oliver Betz <obetz@despammed.com> writes: >> I don't want to tolerate much more frequency deviation to keep a >> certain margin for the fast async serial communication. > > I thought for async you could be pretty sloppy, since the receiver is > edge triggered by the start bit, and you just have to sample from > somewhere in the interior of each of the 8 bits going by. So the timing > could be off by hmm, well, several percent at least.With one start and stop bit each, plus eight data bits, just barely catching the leading or trailing edge of the stop bit means being within +/- 5%. That would be exceedingly marginal. If your hardware is doing the usual majority-of-three voting that trims your margin some (because you want all three samples within the bit), if you're allowing for some lowpass filtering, that'll trim your margin, etc. Just as a knee-jerk estimate I wouldn't be happy unless it's +/- 2.5% overall, which leaves a bit over 1% for each clock if such processors have to talk to each other and you can't assume that they'll track together with temperature. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Reply by ●February 22, 20132013-02-22
On Friday, February 22, 2013 7:33:00 AM UTC+13, Oliver Betz wrote:> Hello All, > > any suggestions for small (e.g. TSSOP20) microcontrollers with a good > on-chip oscillator? > > > One of the best I found is the 9S08 with 1% max. drift in the 0..70�C > range. The 9S08 would do the job but is at it's speed limit.The SiLabs C8051F5xx series, spec 0.5% over �40 to +125 �C, and they are faster than the RS08 ?
Reply by ●February 22, 20132013-02-22
j.m.granville@gmail.com wrote:>> any suggestions for small (e.g. TSSOP20) microcontrollers with a good >> on-chip oscillator? >> >> One of the best I found is the 9S08 with 1% max. drift in the 0..70�C >> range. The 9S08 would do the job but is at it's speed limit. > >The SiLabs C8051F5xx series, spec 0.5% over �40 to +125 �C, and they are faster than the RS08 ?Thanks for you rsuggestion. The frequency stability is even better than their CM3 controllers. But the TSSOP types have very little memory, and I'm not sure whether they are faster than a 9S08 (not RS08). The ADC is much slower. Oliver -- Oliver Betz, Munich http://oliverbetz.de/
Reply by ●February 22, 20132013-02-22
On Sat, 23 Feb 2013 01:50:28 +0100 Oliver Betz <OBetz@despammed.com> wrote:> j.m.granville@gmail.com wrote: > > >> any suggestions for small (e.g. TSSOP20) microcontrollers with a good > >> on-chip oscillator? > >> > >> One of the best I found is the 9S08 with 1% max. drift in the 0..70�C > >> range. The 9S08 would do the job but is at it's speed limit. > > > >The SiLabs C8051F5xx series, spec 0.5% over –40 to +125 °C, and they are faster than the RS08 ? > > Thanks for you rsuggestion. > > The frequency stability is even better than their CM3 controllers. > > But the TSSOP types have very little memory, and I'm not sure whether > they are faster than a 9S08 (not RS08). The ADC is much slower. > > Oliver > -- > Oliver Betz, Munich http://oliverbetz.de/NXP LPC111x is a 50 MHz Cortex-M0. It's available in a 5x5mm QFN and is +/-1% over -40 to 85. It's got a 10-bit ADC that will do 400ksps and has an 8 channel mux out front. -- Rob Gaddi, Highland Technology -- www.highlandtechnology.com Email address domain is currently out of order. See above to fix.
Reply by ●February 22, 20132013-02-22
On Sat, 23 Feb 2013 01:50:28 +0100, Oliver Betz <OBetz@despammed.com> wrote:>j.m.granville@gmail.com wrote: > >>> any suggestions for small (e.g. TSSOP20) microcontrollers with a good >>> on-chip oscillator? >>> >>> One of the best I found is the 9S08 with 1% max. drift in the 0..70�C >>> range. The 9S08 would do the job but is at it's speed limit. >> >>The SiLabs C8051F5xx series, spec 0.5% over –40 to +125 °C, and they are faster than the RS08 ? > >Thanks for you rsuggestion. > >The frequency stability is even better than their CM3 controllers. > >But the TSSOP types have very little memory, and I'm not sure whether >they are faster than a 9S08 (not RS08). The ADC is much slower. > >OliverI've used SiLabs' C8051F061. It has two 1MHz 16 bit ADCs on it -- nobody has them that fast on-chip. But it's internal osc is 2%, sadly. (You absolutely MUST use the DMA to get the data into memory fast enough.) The C8051F5xx is surprising, having the 0.5% internal timer. Looking over the selection guide, I see that the C8051F381 datasheet says "Internal Oscillator: ±0.25% accuracy with clock recovery," and elsewhere, "Internal oscillator with ±0.25% accuracy supports all USB and UART modes." http://www.silabs.com/Support%20Documents/TechnicalDocs/C8051F38x.pdf http://www.silabs.com/Support%20Documents/Software/C8051F380-USB-MCU-overview.pdf The 10-bit ADC is "up to 500 ksps." Jon
Reply by ●February 24, 20132013-02-24
Jon Kirwan wrote: [...]>The C8051F5xx is surprising, having the 0.5% internal timer. >Looking over the selection guide, I see that the C8051F381 >datasheet says "Internal Oscillator: �0.25% accuracy with >clock recovery," and elsewhere, "Internal oscillator withSilabs has several products with internal oscillator being synchronised to USB, e.g. an USB - UART interface running from the internal RC oscillator. Very nice! Grown up with 6502, using 68HC-something and Coldfire (rest in peace) for two decades, I hesitate (but don't refuse) to use 8051 controllers today. My preferred path is ARM Cortex. Oliver -- Oliver Betz, Munich http://oliverbetz.de/
