Hey, i have a problem that i have been at for over a day now, and i can not solve this with my skills. So the problem is as follows. I am trying to get an output from a 4x4 keypad, which would not be a problem but input and output are on the same pins. I know that the 74hc573 should keep the information after LE goes low, but i just can not figure out how to read output from 74hc541 without giving new information to the previous chip, because then the state changes again. At the moment i can only read the keys diagonally, because input and output match in that case. The schematic of the whole circuit can be seen here
:http://i.imgur.com/FWcJRvP.png and the problematic part here :http://i.imgur.com/i7vwFXs.jpg
Hope you guys can give a tip and help me understand this. Thanks
Surely, the whole point of a bus is precisely that multiple things do share the same pins?!
"would not be a problem but input and output are on the same pins"
Why is that a problem?
The input pins are only activated during a write operation, then latched, and the output pins are only activated during a read operation.
I know, at that is what i have been trying to do
while(1) { for(i=0;i<4;i++) { P3_7=0; P3_6=1; in=((0b11110111>>i)&0b00001111); *keypad=in; *led=*keypad; vardelay(100); P3_7=0; P3_6=0; *keypad=0xff; P3_7=1; out=(*keypad&0b00001111); if (in==0b1101&&out==0b1101) { P3_7=1; P3_6=1; lcd_senddata('5'); } else if(in==0b1110&&out==0b1101) { P3_7=1; P3_6=1; lcd_senddata('2'); } }
in=((0b11110111>>i)&0b00001111);
When did Keil C51 start allowing binary constants?
Since i solved this problem