6116 SRAM and 74LS241 Read/Write Circuit in Multisim

Thread Starter

ykbastidasc

Joined Jul 6, 2020
3
Hi, this is my first post in this forum. I get a homework where I'm supposed to use the HM6116A120 SRAM component and a 74LS241 to write values in the RAM memory addresses and then read those values.

I made the following circuit following the 6116 specs but I don't know what's wrong, the data it's set in the bus but I don't know why I can't save the data in the RAM and read it, I would appreciate any help in this issue, I already asked my teacher but my circuit it's exactly the same as the teacher's guide so it's suppose to be "good", but it doesn't work.

1594058828945.png
 

djsfantasi

Joined Apr 11, 2010
6,709
How do you know you can’t save the data? What are you doing to save data?

I have the same questions regarding the read?

One reason may be that in fact, your circuit is not the same...

And it looks like you’re only using four bits. How are the unused inputs connected?
 

MrChips

Joined Oct 2, 2009
21,647
What is the purpose of the signal labeled X1?
Why is the voltage labeled as 2.5V?
Did you know that 2.5V is not a valid logic voltage for 74LSxx series ICs?

What are the requirements of /CS, /WE, and /OE of the 6116 IC?
 

Papabravo

Joined Feb 24, 2006
14,233
Data is written into he RAM on the rising edge of /WE while /CS is low and /OE is high. I bet the switches bounce like crazy -- even in simulation.
 

michael8

Joined Jan 11, 2015
49
> I get a homework where I'm supposed to use the HM6116A120 SRAM component and a 74LS241
> to write values in the RAM memory addresses and then read those values.

Is this a simulation or built?

> I made the following circuit following the 6116 specs

Can the 6116 drive those low value resistors and LEDs?

> but I don't know what's wrong, the data it's set in the bus

The switches don't have a problem handling the current but the ICs may not
be rated for the current the resistors and LEDs take. Or the result may be
that the resulting voltages are too far off due to the load from the resistors
and LEDs for the ICs to work.

> but I don't know why I can't save the data in the RAM and read it,

Assuming it's a real circuit, what test equipment do you have?

I'd measure your 5V supply (should be close to 5v) and also some of the ICs terminal voltages
like U2 (74LS241) pin 18 with key=X on and key=Z off.

Do you know what the "key" switches do?

https://www.idt.com/document/dst/6116sala-data-sheet
https://www.futurlec.com/74LS/74LS241.shtml
 

Thread Starter

ykbastidasc

Joined Jul 6, 2020
3
How do you know you can’t save the data? What are you doing to save data?
...
And it looks like you’re only using four bits. How are the unused inputs connected?
To save the data I close X switch, so the data is put in the cables connecting 6116 and 74LS241, then I close C switch, so WE will be low, according to 6116 specs I need WE low to write in the memory.

The unused inputs are connected to GROUND, the simulator do it automatically so that's why I didn't connect it.

What is the purpose of the signal labeled X1?
Why is the voltage labeled as 2.5V?
Did you know that 2.5V is not a valid logic voltage for 74LSxx series ICs?

What are the requirements of /CS, /WE, and /OE of the 6116 IC?
The X1 was just a probe I was using, sorry I didn't realize that I didn't delete it before upload the photo.
To read: CS should be low, WE high and OE low.
To write: WE low, CS low, OE high or low

Data is written into he RAM on the rising edge of /WE while /CS is low and /OE is high. I bet the switches bounce like crazy -- even in simulation.
That's why I don't get, I use the switches to put WE high, CS is always low (connected to GROUND) and OE it's high cuz I let Z open when I'm writing, but when I open C and X switches and close Z switch to read what I save in the address there is nothing on the LEDS.

Is this a simulation or built?

Can the 6116 drive those low value resistors and LEDs?

The switches don't have a problem handling the current but the ICs may not
be rated for the current the resistors and LEDs take. Or the result may be
that the resulting voltages are too far off due to the load from the resistors
and LEDs for the ICs to work.

Assuming it's a real circuit, what test equipment do you have?

I'd measure your 5V supply (should be close to 5v) and also some of the ICs terminal voltages
like U2 (74LS241) pin 18 with key=X on and key=Z off.

Do you know what the "key" switches do?
This is a simulation, we can't build it in the lab because of COVID. I measured the 18 pin and got 5V with X on and Z off.
I already replied the key switches question above.

Thx to all for your help
 

djsfantasi

Joined Apr 11, 2010
6,709
Pointing out something that PapaBravo said... Data won’t be written when /WE is low; it’s written on the change of /WE from low to high.
 

dl324

Joined Mar 30, 2015
11,250
You can't load the outputs with LEDs and expect to maintain valid logic levels. The address line circuity is questionable. Whether it works depends on the LED forward voltage.

If you really want indicators for address and output, you should add inverters to drive the LEDs.
clipimage.jpg
Your schematic isn't as bad as what many students draw, but it's still messy. You have too many unnecessary wire crossings and jogs. When I was in school, we had to take a drafting class and they taught us how to draw schematics properly.

The next time you post a schematic, print it to PDF so it will be black and white and won't have the grid.
 

MrChips

Joined Oct 2, 2009
21,647
It is not quite obvious what J3, J4, and J5 do, the way you have drawn the circuit.
These are supposed to be switches that pull control signals to GND. Draw them to make this obvious.
The resistors are supposed to be pullup resistors. Draw them to make it obvious.

1594069373314.png
 

Thread Starter

ykbastidasc

Joined Jul 6, 2020
3
Hi! Thanks to all of you for answering, I already solved this, the circuit was good but the problem was with the LED colors, i changed blue ones for orange ones and my circuit worked perfectly. I totally forgot that about the different colors of led, Sorry to bother with this!
 
Last edited:
Top