AFAIK Microchip is the only vendor who has always had a stated policy of short leadtimes, typically
3-4 weeks max on the rare occasions that a part isn't in stock, and a dedicated line to build-on-demand quickly for panic orders. And a track record to back it up. Another thing I read in one of their glossies a while ago is that no single customer represents more than 3% of their business, so less chance of a big order suddenly wiping out a chunk of production capacity. The fact that they have always supported low-volume users means there is plenty of stock out there. The wide range of parts, and general pin-compatibility as you go up the range also means there is often an alternative part that will go in the same socket with little or no software change.
If you're writing in C, the architecture doesn't really make much difference unless you're pushing the limits of code space or speed.
I'd dispute that. In most cases Microchip just add peripherals, leaving the reset the same, as well as keeping the pinout back-compatible. e.g. 18F4520, has the same pinout as the 16C74 four generations ago. Atmel have historically fiddled around with subtle changes in both hardware and software ( e.g. mega8->mega88), leaving a trail of unnecessarily different and incompatible parts in the wake of progress.
I would never be worried about availability issues of a Microchip part (qualifier _once in full production_). Atmel kick ass cost-wise on higher end parts ( e.g. mega88 vs. 18f4520) , but it is yet to be seen whether they have learned from their historical availability nightmares (Anyone remember 52 week leadtimes a while ago..?). Unfortunately Atmel's own devtools suck, and there is no real in-circuit emulator for the current parts. Microchip are streets ahead in this aspect, and for complex projects this alone is a good reason for using them.
Some companies (Motorola, now Freescale) and Atmel have a history of supplying large customers at the expense of smaller ones in times of shortage. Microchip has a business strategy of keeping lead times reasonable (stock to 4 weeks, IIRC). So far, they seem to be doing it. Their customer base is also not as dependent on volatile sectors such as automotive (Freescale) or cell phones (Atmel), AFAIUI.
Best regards, Spehro Pefhany
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If the company is mostly focused on one of the big markets, like automotive or cell phones with short product lifecycles, there is a great change to run into problems sometime later.
For propietary products Fujitsu is a no-go for me. And all the other japanese/chinese too.
They are all companies, that just like us have finite resources, some have different bias to sectors, there is *NO* magic solution (bar having the complete raw materials silicon, gasses, metals to final product under your own manufacturing control). The same as there is no magic technological bullet that solves problems.
What ever company you deal with, will have problems at some time, even if Microchip claim a 4week lead time at max, someone comes along and buys most the stock of a particular part you want, will add a 4 week delay if you hit that delay at the wrong time.
Some sectors like automotive, mean in a product lifecycle, you will still be able to get the parts in 5 - 10 years time. I know of at least one aviation sector project that has an obsolete part that they buy in as a wafer, to then get packaged themselves, as the aircraft is still in production!
If your volume is likely to be large talk early and often with your distributor and manufacturer as this helps in production planning. Who ever the manufacturer is.
My general rule is, when you are small volume try to ensure you have product in your hand before laying out circuit, noting lead time and ensuring you have parts in advance for at least the expected build rate to cover lead time and review your requirements OFTEN.
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I would keep myself from Maxim. They make awesome ICs and they are really nice in providing the samples. However when it comes to the production quantities, you are stuck for the unknown time period.
OTOH, if Sanghe's policy is to build enough excess capacity ahead of the curve, they are more likely to get there. Their costs will be higher than if they aim to minimize capital expenses, but they may be able to gain market share among customers who value availability. Make sense? They can also *decide* not to take all the availability away from the smaller customers when a large customer comes along and wants an unexpectedly large quantity. ie. quote the big guy a bit longer lead time and not screw the smaller guys. It's a business decision, free will, not some free market crap. They can do whatever they like-- chips are not some fungible commodity.
Best regards, Spehro Pefhany
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We have been using a PIC16C54 in a design for about 13 years. We really should update to the 16F54 (it is slightly cheaper!), but we have not had any problems getting the original part. From Microchip.
Yes, Maxim I already know about. I don't actually bear scars from their policies*, but I do suffer some hearing loss from the cries of anguish in neighboring cubes.
I once sat in a room with a couple of Maxim sales guys who said "we never obsolete parts". I think that's true -- they just don't start turning the crank until they have 10000 on order.
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Choosing a processor which can run 'standard' C code will make life a lot easier in the long run (for example: when moving to a new CPU after a few years).
Picking something that is carried by 'next day delivery companies' (Digikey and Farnell to name a few) is usually safe. You can also look at the STR7 series from SGS-Thompson.
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Heck, I recently had an AVR designed out in favor of an ARM7, initially because of the price advantage of the SAM7S64 vs. the ATmega128, but once we compared in detail the SAM7 also used less power at the same clock speed!
I am surprised that no one else recommended an ARM.
I don't know, but I suppose many of us have applications that very low sleep current, which ARM's don't have, or very fast wake up times, which ARM's don't have, or wide operating voltages (e.g., 1.8 to 5 volts for AVR's) which ARM's don't have, or require integrated LCD controllers to drive simple LCD glass, which ARM's don't have. PICs, AVR's,MSP430s, H8's ,8051s, or Elans all have the above features in a wide variety of flavors and tiny sizes.
The ARM is really a different class of embedded processor, higher power, higher throughput, higher speeds, less integrated, requires external regulators etc.
There is some overlap, with certain ARM's under certain conditions, if I remember correctly, the SAM was the only ARM that beat the AVR in active mode but that was only under certain strict conditions (no PLL), the other ARM's had vastly greater power consumption (ADUC7000's for example) making high active power another difference between ARM and the gang I mentioned above.
Thus, although ARM's are nice, they don't cover the same range of applications as the others, it's nice to have one processor that you can use when the power is provided by a coin cell or power mains.
Some of what you say is true, but the apps where the wide voltage range of the AVR is useful is only a subset of embedded apps. It may be that
*all* of *your* apps fall in that category, but that still does not mean that that is a large market compared to the rest.
When you talk about the SAM7 not beating the ARM other than under "strict conditions", you may not understand the SAM7. With the PLL on, it is still lower power than the ATmega128 at the same clock speed. The information I have from Atmel shows the current for the "clock divisor" with the PLL on at under 300 uA or about three times the current for the rest of the circuit running at just under 1 MHz. With the PLL off, the chip current can get below 40 uA at very low clock speeds. Meanwhile, the spread sheet shows the chip drawing 6 mA at
12.5 MHz with PIO, I2C and SPI all running.
The sleep current of the AVR will be lower than the SAM7, but that will only be useful if your sleep ratio is higher than 99% of the time. Also what you say about the "wake up" time of the ARM is not universally valid. For most apps you never have to put the CPU into "sleep", you just slow down the clock with the divisor. It all depends on how deep you need to "sleep".
No, the ARMs of any flavor do not cover the same range as the low power
8 bit processors. But there is a lot of overlap and the ARM is clearly the better in those cases. Part of the selection needs to consider what your last design used (for reuse) and next design will require (again for reuse). For many of us, the ARM is the right answer based on the need to provide more processing power in a small package with low power. Some still need the wide Vin range and ultra low sleep current.
The parts I think will really kick some 8 bit butt is the next generation of CM3 devices from LM. I don't have any hard data yet, but once they target the low power modes I think the CM3 has a lot of potential to do low power "right"! I just hope they don't give up 5 volt tolerance.
The new SAM7L series is claimed to be ultra low power and have LCD drivers, which is the combo I need, but Atmel is also coming out with Xmega AVR's series shortly (from the rumor mill), who knows what features they will have.
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