Programming a Simple Memory
In this article, I showed how to wire a set/reset latch with two NAND gates. Now, let's hook four of these up to create a circuit that can program and write a simple 16X4 memory.
Here is the circuit:
Click for larger image
Here is the fig diagram. For more info on the program that created the schematic, see Xfig.org.
Here is how the circuit looks when breadboarded:
Just tap in four bits. Push the button hooked up to WE on the 74S189, and it programs the current address. Latch the current address by pushing the button hooked up to the CP pin on the '374. The current value of the location on the address latch shows up on the right bank of four LEDs. The address shows up on the left bank. Note that you can also use a 7489 memory. I just happen to have a bunch of 74S189s. I used a '374 because it has an output enable signal, which I could use to share the bus of my circuit with a CPU if needed.
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