16-bits latch ... I2C?

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Hey guys

I'm about to build a giant LED matrix (22x12)
And was thinking about using some 16-bit latch ic controlled over I2C...
(one for the colons and 2 for the rows)

Until now I've only find I2C latch's at TI (texas instruments)
Like this one:
http://focus.ti.com/docs/prod/fo...

But I was thinking if any of you knew some better once ?
Or maybe all ready now could say if its gonna work....

//B4Me

uC's: Atmega16, 32, 64, 128 and Attiny13
Lang.: C
Interests: Small scale robots AND sensor monitoring system

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You could always program a slave AVR to do it. Then not only would you get the latch, you might also be able to put in more functionality that you wouldn't get from a simple latch.

Regards,
Steve A.

The Board helps those that help themselves.

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Koshchi wrote:
able to put in more functionality

Like ?

The only think I could think off was a higher "latch speed"

uC's: Atmega16, 32, 64, 128 and Attiny13
Lang.: C
Interests: Small scale robots AND sensor monitoring system

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What about 74HC595? I'm using that to control 7 segments. control over just 3 lines and can put those in a row as many as you like. They are fast too.

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One of my personal favorites - the Allegro A6276. A 16 bit serial constant current LED driver with outputs that can stand 16V and need no series resistors. You can drive a string of them in series off the SPI port as fast as it will go - much faster than I2C. There are pin-compatible equivalents from at least two other manufacturers.

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Hmm don't you think 400 KHz is enough, to drive 3 I2C devices ?
it gives like 44KB/s

I've never done this before so if you think it's to slow, say it ?

uC's: Atmega16, 32, 64, 128 and Attiny13
Lang.: C
Interests: Small scale robots AND sensor monitoring system

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As stated above you could use an avr with 18 I/O like ATmega8. The extended functionality depends on what you want to get out of your circuit. I think that the price beats the "functionality" because an I/O expander costs more than an small avr, but you'll have do do some intensive thinking if you choose slave avr.

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I think I'd have to go with Perets suggestion.

Whether you use an AVR directly or, some sort of serial latching device, you will still need to consider some sort of driver as, the AVR probably won't handle the current demand of all of the LEDs on it's own.

The Allegro A6276 will do the job of two 74HC595 8 bit latching shift registers, as well as provide the serial interface, latches, and as a comon tunable current source. In addition, the Allegro A6276 is expandable, in that, it also incorporates a serial output, allowing expansion to multiple devices.

The only real trade-off might be cost, as opposed to that of some of the other methods that have been mentioned, or that are available.

As I am always intreuged with new technology (not that this is new, but different), I would consider this as a viable alternative to anything else.

Isn't technology a hoot??? You usually have multiple ways to accomplish most anything!!!

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Quote:
Like ?

The only think I could think off was a higher "latch speed"


Don't know what you want to do with that LED matrix...
But since a slave AVR would have the same intelligence as the master you will have more computing power to do stuff that one intelligent chip couldn't pull off. You can maybe also shorten messages needed to be sent from master to some sort of commands interpreted by the intelligent slave. If this is useful all depends on what your matrix is supposed to do.

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Hi and thx for all the replys.

I've just ordered some sampels of PCA9539 there is a I2C Latch...
If this don't work I'll try "Allegro A6276"

I have a LED uC (mega32) to handle all the latch controling...
And another mega32 for handling of the sensor data and other stuff....
They will talk internt via SPI (I hope)

uC's: Atmega16, 32, 64, 128 and Attiny13
Lang.: C
Interests: Small scale robots AND sensor monitoring system