Alternative to 74HC244 extra digital inputs
Posted: 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! )
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.
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! )
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.