hellothe project is cascade 74hc595 SER to PARALLEL ,my project is working fine but my prob on start up power, all data output is low logic that mean relays is close and others data , on init mcu i am CLR data output but the same prob some one to help regards jamalo
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Connect all the /OE signals to an MCU I/O pin and use a pullup (10K is fine) to hold this high as the power comes on. The relays will stay off until your program can initialize all the shift registers, then set the I/O pin for the /OE to low.
This thread moved to General Discussion. It doesn't belong in the Projects forum.
and how are , i am realy happy for your help thanks very much
your Idea is very good to control by OE/ also during power lose or cut off by mcu funtions save data and off reayls , but after i wrote my thread here i pull down latch data line on that i solved my prob how about this point , we are waiting your respond
regards engineer jamalo
The problem with your solution is that the latches can have either state (0 or 1) on power up. Often they're designed to favor one state or another when they're initialized, but the NXP datasheet for the 74HC595 doesn't say if this is the case and, even if it were the case, some other manufacturer may do it differently.
If your solution works for you, keep it. If you were making a commercial product, I'd say you should use my solution or check with the manufacturer about the initial state of the latches.
yes i did that with MR/ also that very good , we are making robust sys product its kind of lift board , we have to study robust sys and all Possibles like ESD /EFT PCB ,do you think that scan sys by 74hc595 for write data out and 74hc165 for read data are convince and robust , or do you have other Idea , i am very sorry for your time ,
waiting your respond
regards engineer jamalo
mselaf@yahoo.com
your respond ,you are Handsome man thanks
regards engineer jamalo
email : mselaf@yahoo.com
Fyi, all the shift registers I've tested (74HC164s and 74HC595s from TI) have a power on reset circuit. This circuit arms when Vcc drops below ~1.8v with 74HC series, and triggers when Vcc rises quickly past this threshold. The results of the power on reset are the same as toggling the /MR line.
Lawson
Lawson
I know your comment was mostly in jest, but there's no secret handshake.
I don't know how else to state it, but why would the makers of, say, a Static RAM chip list as a bullet point feature:
* state of each bit is indeterminate on powerup. Some of your previous data from before might be there, but who knows?
It's basically "don't assume the powerup state of any type of memory device (flip-flop, latch, etc) unless it is specifically defined".
This goes doubly so for unitialized program variables: sometimes they will be said to be set to 0, but rarely will they say that they aren't set to a specific value.
Oh now I am little confused .our project ( mcu :16f877A crystal :20Mh )
its just little confused about 74HC595 and 74HC165 are suitable to our project or not that is . i am realy soory for your time
good luck
i think its suitable
Good luck,
FF
During initialized time mcu can enable and disable data output (595) by control OE bit or any other external hardware also pulldown resistors to establish a known output state for an I/O
But we are encounter fatal error :
If mcu is victim by spikes or rest state , that mean we lose connection data scan sys by output data on that MR don’t effects any way but only OE/ is effects on that any external hardware can disable relays output.
regards engineer jamalo
this code during interrupt scan 10Ms
//++++++++++++++++++++++++++++++++++++++
// DISABLE OUT DATA SCAN
if(!RELAYS_DATA)OE_595 = _595_DISABLE;
else OE_595 = _595_ENABLE;
//++++++++++++++++++++++++++++++++++++++
write_expanded_outputs(data_595);
regards jamalo