And now, the RAM memory of my SAP computer is done. Two 74LS189 IC's 64-bit RAM memory is used in this project. This memory have 16 address of 4 bits wide, so with two IC's we have a memory of 16 address of 8 bits. An circuit of selection has been implement with multiplexers, to make  PROG mode (manual programming) and RUN mode (runtime programming) of RAM memory module. So, with the PROG mode selected, we can input manually the data at specified address of RAM using DIP switch, to program RAM more easily. The Memory Address Register (MAR) is implemented, that transfer the address from the BUS to setting of memory address in RUN mode. With /RAM_OUT control bit we can transfer the 8-bit data of RAM to BUS, and make another operations. This control bit, and others,  will be used with the Control module, that will be constructed further up, when the execution of program stored into RAM will happen.

The video bellow show all the process of RAM memory step by step.

Note: This video have English subtitle, that you can activate on You-tube Player.