Alternative to 74HC244 extra digital inputs

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Jay Dee
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Alternative to 74HC244 extra digital inputs

Postby Jay Dee » Mon Jul 16, 2012 6:58 pm

Hi,
I've been trawling and sent myself to sleep reading datasheets but someone here may know this already. :)

I want a simple method of polling 32 digital inputs using a single 8 bit port. - (simple and rubust is key! :wink: )
So... use 4 x 74HC244 (Non inverting input buffer with enable), 8 digital inputs go to each chip. Each chip has an enable pin, select and read each one in turn.. nice simple solution.

But I cant find a version with all the inputs on one side of the chip and the outputs on the other, thus giving a much tidier PCB layout.
I also understand that multiple 74HC244 can add to much capacitance to the bus. The digital states being read will be very slow (mechanical switches ) but I would still wish to select and read each chip each one at a decent rate.
Any Ideas?

I was avoiding using the 74HC574 but currently looks the most promising.
I could also use an input expander using SPI but I've already got loads of SPI devices and routing the tracks to so many devices could get messy.
:?
John.

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Re: Alternative to 74HC244 extra digital inputs

Postby Jay Dee » Tue Jul 17, 2012 11:50 am

Ahh fresh look today.
74HC541 looks like a go.

> All inputs on one side, outputs on the other.
> Schmidt input behavior (Hi State at 3.15V [4.5V Vcc] Lo State at 1.35V [4.5V Vcc])
> Enable pin (Pull pin Lo to Enable)
> All pins are Tri-State when disabled (Off Bus)
> Easy to solder SOIC Package (1.27mm pin pitch)
> 2 to 6 V supply, nom 5V.
> Just 6ma output drive.

Will give this a go I think.
J.
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Re: Alternative to 74HC244 extra digital inputs

Postby Jay Dee » Tue Jul 17, 2012 11:56 am

Oh forgot..
Texas SN74HC541DWR
Farnell 1607638
40p each or 23p for 10+
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Re: Alternative to 74HC244 extra digital inputs

Postby Steve001 » Mon Jul 23, 2012 6:44 pm

Thanks for that one project i have lurking i needed 40 inputs :? (Ribbon cable tester)

will look into that later :D :D :D :D


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Re: Alternative to 74HC244 extra digital inputs

Postby Steve001 » Mon Jul 23, 2012 7:37 pm

there is also a dip version

FEC 380817


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