|31.25Khz to 4Mhz||Internal RC||Very Poor (+/- 8%)||low||Zero!|
|? to 1Mhz||External RC||Terrible||low||cents||R between 3K and 100k C between 20pF and ???|
|1Khz to 50Mhz||Crystal||Best!||med||low||We recommend 50MHz fundamental mode crystals from Abracon (firstname.lastname@example.org, (949)448-7070). For low-profile thru-hole, use ABL-50.000-F (3.5mm height) or ABL2-50.000-F (2.5mm height). For low-profile SMT, use ABLS-50.000-F (4.2mm height) or ABLS2-50.000-F (3.3mm height). Please refer to Abracon's Web site for specifications (http://www.abracon.com/).|
|2Mhz to 50Mhz||Resonator||excellent||high||med||The Murata 50 MHz resonator (Murata CSTCV50.00MXJ0H3) is recommended
to be used with SX devices. This is a newer and better part.
|1Hz to 100Mhz||Oscillator||varies||varies||high||Frequencies higher than 50MHz require the use of a TTL Clock Oscillator as the clock source. For example ASL or ASF family from Abracon or PLL IC. Digikey has (or had) CTX121-ND (50Mhz, 40mA) and the Epson SE2911 (75Mhz). At these frequencies the SX should be configured at the highest gain settings, OSCHS2 or OSCHS3. Be very carefull to unplug the OSC when programming the SX as most will be destroyed by the programming voltage (about 13V)|
Stephen Holland says:
There are several ways to get a clock... A few of the more popular ones are listed below.
- Crystal Oscillator - the 4-legged can. There are thru-hole versions which are generally called 'full size' (rectangular) or 'half size' (square). Various companies offer surface mount as well. Generally, they are a good solid clock, but also can be very power hungry. A quick search of Digi-Key found the CTX MXO45-50.0000 (Digi-Key # CTX121-ND), which consumes ~40mA at 5V. This is on top of the power consumed by the crystal driver within the SX, which is still required. This type of oscillator is harder to find at lower voltages, and as it is a hard driver output, they generally cannot accept higher than 7V on the output pin. This is one good reason why the oscillator must be removed from the OSC circuit when the SX-Key is programming or debugging (it puts Vpp = ~12.5V on OSC1). Only requires to be connected to OSC1 only.
- Crystal - The most accurate type of clock source. To use on the SX, it will need to be a fundamental mode. Most uControllers require fundamental mode anyway (3rd overtone is possible, but with the required LC filter circuit to be stable, it becomes too expensive), the reason it is mentioned specifically is that relatively few companies offer fundamental mode crystals above ~40MHz. Abracon (www.abracon.com) is one such vendor, as has always been quick with samples for the SX. Check out their ABL (HC-49), ABL2 (HC-49 low-profile), ABLS (AT49 SMT), ABLS2 (AT49 SMT low-profile), ABM5 (SMT ultra miniature) and ABMM (SMT micro miniature). Crystals, because of their high accuracy, are really required for applications where timing is absolutely critical.
- Crystal Resonator, Ceramic Resonator or just Resonator - A little more drift (less accurate) than a crystal, but smaller and sometimes cheaper. Again, relatively few companies offer fundamental mode resonators above ~40MHz. Murata is a good source of resonators, and offer versions with and without built-in load caps in various packages. The names for the various families Murata offers are (the info I have is a couple years old, but should still be good): Thru-hole without caps - CSA, thru-hole with caps - CST, SMT without caps - CSAC, SMT with caps - CSTCC.
We recommend 50MHz fundamental mode crystals from Abracon (email@example.com,
(949)448-7070). For low-profile thru-hole, use ABL-50.000-F (3.5mm height)
or ABL2-50.000-F (2.5mm height). For low-profile SMT, use ABLS-50.000-F (4.2mm
height) or ABLS2-50.000-F (3.3mm height). Please refer to Abracon's Web site
Richard Ottosen [rottosen at IDCOMM.COM] says :
A third overtone crystal on the [SX] can interfere with the oscillator pins when they are used to program the SX. The inductor of the filter for third overtone operation can short the programming voltage and damage the SX or the programmer! [ed: Use a large value cap (0.1uF or so) in series with the inductor to remove the un-necessary DC short.see http://www.saronix.com/pdfs/128/128.p1.pdf]
The Murata 50 MHz resonator (Murata CSTCV50.00MXJ0H3) is recommended to be
used with SX devices. This is a newer and better part.
Frequencies higher than 50MHz require the use of a TTL Clock Oscillator as
the clock source. For example ASL or ASF family from Abracon or PLL IC (ICD2053
from Cypress). At these frequencies the SX should be configured at the highest
gain settings, OSCHS2 or OSCHS3.
Ted Inoue says:
I had been having problems with intermittent problems with some of the boards I'd developed using the SX chips. They'd work fine using the SX-Key, but when using a resonator they'd either fail to start up at all or would only do so randomly.
After troubleshooting and help from those on this list (thanks guys!) I tracked it down to improper reset on power-up. I'm pretty certain that the chip was slowly coming on as the power cycled up and was unstable.
There were excellent suggestions about time delay startups, RC filters etc., but since my boards were already built, I needed a software solution. After reading the spec sheets carefully, I tried using the brownout reset fuse, which I'd disabled previously. I enabled the 4.2v setting and instantly all my boards began working 100%.
There's very little information that discusses the brownout option, and it's so useful that I thought I'd pass this along. It's made the difference between having a (commercially) useless product and having one that I can comfortably put into users' hands.
I'm working on a project that has 16 SX28 ucontrollers in it. Each chip is clocked by a 20 mHZ surface mount resonator, all of which were purchased from the Parallax website. My problem, is that when the system is powered up, some of the ucontrollers don't respond correctly to asynchronous communications. Therefore, I checked the clock frequency, and found that the clock frequency (provided from the 20 mHz resonator) of about 1/4 of the chips is about 34 mHZ! It seems totally random; each time I power-up the system, different resonators are running at this higher frequency, and sometimes they all start up correctly. The rise time of my power supply is about 16ms, and I've placed a 1 mohm resistor across the oscillator inputs of each of the SXChip/Resonator pairs. Has anybody seen a problem like this? Any ideas? Thank you very much!
James Newton replies: Try changing the osc drive settings in the programming of the sx28's e.g. from HS to XT2 spamryan at TakeThisOuTflyingrobots.com replies: "Thanks James! That solved the problem that has been keeping me from finishing this project for days! Thanks a lot for supporting the SX List - it's very helpful!" +
I was under the impression that Ubicom had abandoned support
for the SX processors. Furthermore, they seem to be hard to
get, and quite expensive. I do have an SX-KEY and SX-Tech
development system, but have been shying away from the SX chips
because they seem to be fading away.
I welcome comments.
James Newton replies: Nope, Ubicom supports the SX chips nicely, thank you. There have been some shortages, but they are available and the cost is not bad at all considering what you get. I don't think they will fade away until there is another microcontroller than can run at 75 MIPS!+
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