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Author Topic: Is there any difference between the max485 chip versions?  (Read 802 times)
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I see sellers listing different versions of the max485 chip. Does it matter? I want to make sure I don't buy the wrong thing. So far I have come across a:

MAX485CPA MAX485EPA MAX485CPA+ MAX485EPA+ MAX485CSA MAX485ESA

I can't really tell from the spec sheets what the difference is. There also seems to be huge disparity in prices. Like this vendor has 50 chips for $9. That's allot of chips!

http://www.ebay.com/itm/50pcs-MAX485CPA-MAX485-RS-485-RS-422-Transceiver-/390476689431?pt=LH_DefaultDomain_0&hash=item5aea397017

or 10 for $2.... are they really that cheap?

Thanks
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The letters after a part number normally specify the package they are in and the temprature range they can operate at. Sometimes it will also denote the speed.

Are they that cheap? They can be if they are surplus, out of spec devices from the reject bin, or have not been payed for. Bulk prices are often quite cheap and $0.20 each for that type of chip looks to me like it is the 100,000 up price.
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Thanks for the clarification. They all look the same in pictures so it sounds like it won't matter much. For $0.20 I guess I can't really go wrong. Hopefully these chips will allow me to daisy chain my tlc5940s out to a usable distance.
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Quote
Hopefully these chips will allow me to daisy chain my tlc5940s out to a usable distance.
Possible not, these are slew rate limited drivers. The slew rate is the rate of change in voltage. That means the rise and fall time of the signals is deliberately slowed down. This is fine when driving serial coms data but it will limit the top frequency you can send down them. Check first what the top frequency of the TLC5940 needs to be, this will be the clock. Then calculate what the maximum frequency of these drivers is.
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The TLC5940 does like 30 MHz, the Arduino's can only send SPI out at 8 MHz.

http://datasheets.maximintegrated.com/en/ds/MAX1487-MAX491.pdf
Page 15 explains what the letters at the end mean - package type, temperature rating

MAX485 is not slew rate limited, others on the data sheet are.
MAX488 allows full duplex operation 485 is half-duplex only.

Min supported data rate 2.5MHz -max dependent on wiring in use, better quality & good terminations will yield better results.

Good application note:
http://www.maximintegrated.com/app-notes/index.mvp/id/763
« Last Edit: November 16, 2012, 04:23:41 pm by CrossRoads » Logged

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My plan was not to link the TLCs directly with the max485s (sorry I realize my post was vague). I plan to have an atmega328 at each location which will interpret the serial commands sent to it by the arduino master through the max485, and then it would in turn tell the TLC at its location which LEDs to turn on. So each node will contain a atmega328, a TLC5940, and a max485 plus  (crystal, resistors, pins etc).

I only need to tell the slaves what to do and do not need them to talk back to the master so half duplex should be fine right? The whole reason for me going for this node based approach to begin with is to cut down on the wiring needed.

Please tell me I have not misunderstood this whole thing, I have a pile of chips on order smiley

Thanks for you help guys, the bit about the clock speeds really shed some light on a bunch of blank spots I had in the way these pieces interact.

-Sathi
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OK that sounds alright.
It is called just one way, not half duplex if the slaves never talk back.
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OK that sounds alright.
It is called just one way, not half duplex if the slaves never talk back.

The 'official' term for a communication link that is one way only, is a simplex link.
http://en.wikipedia.org/wiki/Simplex_communication
Lefty
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The letters after a part number normally specify the package they are in and the temprature range they can operate at. Sometimes it will also denote the speed.

Are they that cheap? They can be if they are surplus, out of spec devices from the reject bin, or have not been payed for. Bulk prices are often quite cheap and $0.20 each for that type of chip looks to me like it is the 100,000 up price.

I know this is an older thread, but is there a possibility of counterfeit max485 chips or is that a myth?  I am seeing (50) max485cpa+ dip-8 chips for $7.64 USD including shipping, which would be 15 cents a chip.
http://www.ebay.com/itm/50-PCS-MAX485CPA-DIP-8-MAX485-RS-485-RS-422-Transceiver-/291093970281?pt=LH_DefaultDomain_0&hash=item43c68d7d69

thanks,
Mike
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Incredibly cheap prices are a good sign that something is not legit.
Buy your parts from digikey, mouser, someone that has traceability back to the manufacturer.
Digikey, Mouser, Avnet, Newark, all show this part as a $2+ price/chip in 50-lots.

Or take your chances.  A real company would not buy parts from e-bay. A hobbyist certainly can. At worst, you lose some time debugging & stuff, finally determine you got hosed and go get real parts.
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Arduino for Teens available at Amazon.com.

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