Has any One Used this Before .Allegro A6276 16-Bit Serial Input, Constant-Curre

sam_sam_sam

Hi Every One

Has any One Used this Chip Before

Can this be used with Basic Stamp

http://www.allegromicro.com/en/Products/Part_Numbers/6276/6276.pdf

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Sam

Mike Green

This looks functionally similar to the 74HC595. I didn't compare the pinouts, but I'd suspect they are the same. The 74HC595 uses positive edge triggered clocks and the Allegro datasheet seems to imply that the part uses high level clocks, but functionally it shouldn't matter.

sam_sam_sam

Mike Green

Thank you for your reply

Is that to· mean that·I should be able to use the 74HC595 Demo as a starting
point to begin to use this chip



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Sam

Mike Green

I looked again at the datasheets. The pin-out is completely different, the Allegro part is 16 bit and the 74HC595 is 8 bit, but functionally they look much the same. You might be able to use the 74HC595 demo and it should look as if you had two cascaded 74HC595 devices.

sam_sam_sam

Mike Green

Thanks for your help

I will give this a try

I will look at both Data sheets and see what i come up with

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Sam

MikeK

The 74HC595 doesn't have the constant current outputs that the 6276 has.

whicker

yes, I've used the A6276, and it works fine.
it's useful to get away from the annoyance of having to select the current limiting resistors (you just pick one resistor to set the current for all outputs).
Plus, with most of my mixed LED's being the water-clear lens variety, you can't tell the color until you turn it on.

keep in mind it's a current sink, unlike the 595. This means you can use a higher voltage on the anode of the LED (+5V) to deal with the blue LED's and such, with the rest of the system at 3.3V. Any RGB led's would need to be the common-anode variety.

sam_sam_sam

MikeK

Thanks for your reply

Iwill keep that in mind when i look at the two data sheets



whicker

Thank you for your reply

Do you have working code that used for that chip that you do not mind sharing

I will keep this in mind so far i have not used etheir chip

keep in mind it's a current sink, unlike the 595. This means you can use a higher voltage on the anode of the LED (+5V) to deal with the blue LED's and such, with the rest of the system at 3.3V. Any RGB led's would need to be the common-anode variety.

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Sam

sam_sam_sam

Mike Green

Had little time to look at both data sheets



The pin are as folllow

On the A6276···························

Pin 2··· ·Serial Data In··················

Pin·3···· Clock···························

Pin 4··· Latch Enable



····On the 74HC595··········································

·Pin 10······ MR Master reset··
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·Pin· 11····· SH_CP Shift register clock input·
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·Pin· 12······ST_CP Storage register clock input·
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·Pin· 14······DS· Serial Data Input·························

I can see that some pin are the same

On the A6276······ ·Pin ·2····· ·Serial Data In·

·On the 74HC595···Pin· 14······DS· Serial Data Input··



Now the 74HC595·has two clock pins where as the A6276 has one clock pin

·On the A6276··Pin·3····Clock

·······································································
On the 74HC595··

·Pin· 11····· SH_CP Shift register clock input·
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·Pin· 12······ST_CP Storage register clock input·

Now on the 74HC595 has a Pin 10· MR Master reset·

Which the A6276 chip dose not

What do· i have to change to able to get the 74HC595 demo to work on the
A6276 Chip

Thank You for any help that you can give me in this matter

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Sam

Post Edited (sam_sam_sam) : 3/2/2008 1:37:32 AM GMT

whicker

tie output enable low

just translate my pseudocode into a program:

start out program with clock, latch enable, and data pins low.

repeat 8 times:
set your data pin (1 or 0)
set clock high
clear clock low

set latch enable high
clear latch enable

end

really, that's it.
just expand from that basic code.

sam_sam_sam

whicker

I will give this a try when i get one of these chip I hope it will be very soon
Thanks for your help

repeat 8 times:
set your data pin (1 or 0)
set clock high
clear clock low

set latch enable high
clear latch enable
end

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Sam

Branmuffin Industries

Hey everyone,

I think it's really cool that I can find another group out there interfacing the Propeller to the A6276. I have an A6276 here and I've been trying to get it to work for days. It's like beating my head against a wall!

Now that I've read the progress you guys have made, I can probably get it done.

A few questions:

on this pseudocode:

repeat 8 times:
set your data pin (1 or 0)
set clock high
clear clock low

does "clear clock low" mean the same as "set clock low?" i use these lines to set the output:

outa[noparse][[/noparse]debug] := 1 'sets high
outa[noparse][[/noparse]debug] := 0 'sets low

I can't get the A6726 to respond, so I'm wondering if there is a problem that the A6276 needs 5v/GND serial pulses and the propeller can only put out 3.3v/GND serial pulses. Can anyone verify that it works with the 3.3 v pulses directly out of the propeller?


I also see you guys saying that the A6276 SINKS. Does this meanin the LED array needs to have a common +5v supply, and then I set it up to sink individual grounds using the A6276 pins?

I will let you guys know how it progresses, and post my code as an A6276 object file for all to enjoy.

Thanks

-Ryan Brandys

Bruce Bates

Ryan -

You may want to ask to have this post moved to the Propeller Forum, so the folks who use Propeller chips can assist you. You will probably get a faster answer too.

Regards,

Bruce Bates

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Programming can't be all that difficult, it's nothing but 1's and 0's

whicker

There is nothing unique about this chip and its operation in general, other than its constant current sinking outputs.
It is a simple serial to parallel shift register, with an output latch stage.

Branmuffin Industries:
yes to all of your questions,
yes I was being redundant in saying clear = low = 0, and set = high = 1.

yes with the propeller you need to power the chip's VDD (pin 24) with 3.3 volts, not 5.0 volts.

yes, because this again, sinks current, you can connect your LED's anode to whatever voltage you want, provided it will "eat" a majority of the voltage. The cathode will go to the output pin. What I'm saying is, a red led might need only 1.7V@20mA to light up, why connect its anode to 5V when you have a perfectly good 3.3V supply? On the other hand, if you've got a white LED that lights up at 4.2V@20mA, then you'll want to use the 5V supply you're talking about. The 5V would go to the anode of the LED, and the cathode would go to the output pin. This seems wrong, but it's not because again these chips SINK current, not SOURCE it. The '595 is a normal voltage source. In the '595 the output pin would send current through a resistor to the anode of the LED, and the cathode would go to GND (or VSS).

As for why it's not working, it could be anything, look at the datasheet for descriptions of each pin:
Did you have a resistor on pin 23 to set the current? For 20mA, it's about 1K.
Is pin 21 (Output Enable) tied low?
Is Latch Enable (pin 4) going high when done shifting? Granted for testing you can just tie this high (to the same voltage powering VDD) with a wire.
pin 1 is connected to your GND (on the propeller protoboards, it's called VSS)?
Are the LED's facing the right direction?
Is your propeller code remembering to set the relevant DIRA bits to 1, to make the pins outputs?

Hope this gets you up and running. Remember you can shift (clock) as many times as you want before latching, but I chose 8 times just to get started. You could even shift once and then latch, slowly, to get a marching LED pattern going.

Branmuffin Industries

thanks whicker. i got it working now. i had to bring the output enable high, then pulse the clock pin, then pulse the latch pin, then bring output enable back low.

tried supplying pin 24 on the chip with 3.3v, and the chip won't power up. the chip wants 5v. i used a 470 ohm resistor to ground and Rext, and it seems to work OK.

The next problem i'm working on fixing has to do with BITWISE SHIFT LEFT versus BITWISE ROTATE LEFT. my understanding is that if I:

X >>= 1 then that is a bitwise shift where the data on the leading end is destroyed, and the trailing end adds a zero
X ->= 1 then that is a bitwise rotate, where the data on the leading end wraps back around to the trailing end.

I have tried both of these and they both act as bitwise shift. the bitwise rotate loses the data and does not loop it back around.

has anyone else ever had a problem with this?

-Ryan