mstechca
New Member
I am trying to build my own ROM programmer for the 28C64 EEPROM.
However, I have one question.
In order to avoid using an OR gate or 2 diodes, I was wondering if it is electrically safe to connect two outputs and one input together.
The outputs are 1 output from a CMOS 4081 AND gate, and one output from the CMOS 4017 counter. No more than 5V is flowing through the entire circuit. The input is the enable pin from the counter.
Why do I have this setup? because there are two things that can prevent my counter from moving on to the next stage. One is when the counter reaches the end, and the other is when the ROM is in read mode, and valid data isn't received.
I can understand if I need to waste a chip for an XOR or an XNOR gate, but it is ridiculous to use one for an OR gate, if I don't have to.
And I was wondering if I could get away with a 200uS timer.
In other words, If I set the "WE" pin low for 200uS, then the "WE" pin high for 200uS, and then the "OE" pin low and left "OE" low, will the data I/O pins eventually return whatever data I fed it when "WE" was low? or is it more complex?
However, I have one question.
In order to avoid using an OR gate or 2 diodes, I was wondering if it is electrically safe to connect two outputs and one input together.
The outputs are 1 output from a CMOS 4081 AND gate, and one output from the CMOS 4017 counter. No more than 5V is flowing through the entire circuit. The input is the enable pin from the counter.
Why do I have this setup? because there are two things that can prevent my counter from moving on to the next stage. One is when the counter reaches the end, and the other is when the ROM is in read mode, and valid data isn't received.
I can understand if I need to waste a chip for an XOR or an XNOR gate, but it is ridiculous to use one for an OR gate, if I don't have to.
And I was wondering if I could get away with a 200uS timer.
In other words, If I set the "WE" pin low for 200uS, then the "WE" pin high for 200uS, and then the "OE" pin low and left "OE" low, will the data I/O pins eventually return whatever data I fed it when "WE" was low? or is it more complex?