[SOLVED] Using AT89S52 and 74HC595 "Daisy chained"

[wicus]

I'm used to doing projects using only the AT89s52/53 from ATMEL. From one of my kids school projects they want to control about 300 I/O ports using 74HC595 in a daisy chain configuration ?

Will it be possible to do something like this, or will it be better/possible using PIC microcontrollers ?

I will sort out the coding myself, but first would like to know of this can be possible - this will be like a 300 light "string light" with various patterns, where the AT89S52/3 via the 74HC595's control in the region of 300 I/O ports - no inputs will be done on those ports, only outputs

Kind regards

 

[udayan92]

As per this:
https://electronicsmaker.com/em/admin/pdf/free/PORT.pdf

For one connection to the input port,you can control 8 output ports.Assuming AT89S52 has 4 output ports,by connecting a 74HC595 to each of them,you can control 8*4=32 ports.Now if you connect again 74HC595 to every one of them,you can have 32*8=256 ports. It is possible,but port addressing would be very tough.

 

[KlausST]

Hi,

It is possible to daisy chain the 595.
Connect the controller serial data output to the first 595 data input
Connect each 595 output to the next 595 input.
Connect all control lines in parallel.

For 300 io ports you need 300/8 = 37.5 ==> 38 pieces of 595.
Mind that the data_setup_before_clock time needs to be added with 37 x data_input_to_data_output time.
This decreases clock frequency.
Also take care of driving 38 control lines in parallel, here you may need buffers.

If i remember right, then in datasheet of 595 there are schematics on how to daisy chain them. There are many manufacturers for 595, some provide more information in the datasheet than the other. Check datasheets of various manufacturers.

If this solution is too slow, then you might build 4 daisy chains with 5 pieces of 595 each, connectet to one 8 bit port of your controller.
Even with software controlled transmission you may get a higher update rate.
But calculate this before building your hardware.

Klaus

 

[wicus]

Thank you Klaus - Much appreciated. This was exactly what I was looking for.