Learning...

[Bob Upstairs]

As a electronics student I'm trying to do assignments, not learn a software program... How does one go about programming a memory chip in multisim? I learning electronics and don't write code. I'd like to just build the truth table into the thing. Anybody?

Bob

[lacy]

On this one I am a little stumped. I do not know of anyway to put content into memory IC's without going through the MCU Module and either programming it through code or loading a hex file into it.

If there is another way, I do not know of it.

[yyao]

Hi Bob,

Memories are complex devices and simulating them can be vert tricky. Can you give us a better idea of the memory that you are looking for?

How many words (i.e. memory locations) do you need in your memory? How wide do you need each word in your memory to be? Can this memory be read only? What kind of simulation are you going to perform on this memory? Do you need a parallel (DRAM or SRAM type) or serial interface (I2C, SPI, etc)? Do you need a dynamic or static or non-volatile memory or does it not matter?

Thanks.

[Bob Upstairs]

I've been trying to reply but every time I hit 'Submit Post', the system tells me I'm not logged in.

*********worked that time*********

Message Edited by Bob Upstairs on 11-29-2008 07:55 AM

[Bob Upstairs]

Thanks for your reply. My project is a vending machine for a basic logic course. I have a selector matrix that outputs a 4-bit item ID. I wanted to use that as an address for memory to give the price of the items (9 items, 5-bit coded prices). Not too much memory required. Parallel I/O. Type does not matter - it will never go into production!

I have some other memory applications - change making (value-to-coin conversion), and cash display (5-bit coded cash-to-BCD).

I could build a diode matrix but I quickly exceed the limit of components allowed in my student version.

Any ideas are greatly appreciated.

Bob

[yyao]

Hi Bob,

Although your question does not pertain directly to the use of of Multisim, I can make some suggestions.

It seems that you want to implement a look up table. You can easily make a lookup table by using a bunch of multiplexors. For each bit of memory, you need a multiplexor such as the 74LS151. The pins A, B and C make up your memory address inputs and you can hard code the inputs (D0 to D7) to your memory contents. You can also connect multiple multiplexors together to make a larger memory or wider memory. This site also provides some insight to this question:

http://web.cs.mun.ca/~paul/cs3724/material/web/notes/node7.html

[Bob Upstairs]

Yes, thanks. There are several ways I could implement these circuits. But I had it in my mind to hit a memory with an 'address' and come out with a value. I did get the 'memory' for the "item to price", and "item to 2s complement" for the change part, built with gates, however, the change-to-coins logic is a big table and I can't get very far without running over the Student Edition component limit. Maybe I'll just submit the tables...

It's my first logic course and I might be over-thinking the whole thing!

Thank you very much for your help.