Using SRAM

[Rasenger]

Hi!

I'm building a simple "computer", and I'll use SRAM as video ram and also on the mainboard as a communication register between different parts of the computer. The problem is, I haven't found any examples of how to use SRAM with microcontroller. Of course I've checked some datasheets but they are not very beginner friendly. Could anyone point me to right direction?

I'd also like to know if there are SRAMs where can be written to and read from simultaneously..? If I understand right, only one device can read from SRAM at the same time, so different devices should communicate and decide when to access ram to avoid conflict..?

 

[dknguyen]

Hi!

I'm building a simple "computer", and I'll use SRAM as video ram and also on the mainboard as a communication register between different parts of the computer. The problem is, I haven't found any examples of how to use SRAM with microcontroller. Of course I've checked some datasheets but they are not very beginner friendly. Could anyone point me to right direction?

I'd also like to know if there are SRAMs where can be written to and read from simultaneously..? If I understand right, only one device can read from SRAM at the same time, so different devices should communicate and decide when to access ram to avoid conflict..?

Pick an SRAM, and look at the datasheet. It should have the wiring you need. The coding is a different matter entirely if the processor wasn't designed for use with SRAM and you are using it in "real-time" since the coding foudnation doesn't exist and you have to make it. It's mainly just a lot of work with the digital port isn't it? Setting pins high and low to control the RAM based on it's datasheet and doing the same to send data, and reading the port and writing the value to a register to read data?

Don't try going for dual-port SRAM- it's ridiculously expensive- really really really expensive. In fact, SRAM is really expensive too if you need anything more than a couple of K. You might try going for a processor and using DRAM instead as it is much much cheaper and the processor probably has the refresh circuitry built into it.

 

[Nigel Goodwin]

Hi!

I'm building a simple "computer", and I'll use SRAM as video ram and also on the mainboard as a communication register between different parts of the computer. The problem is, I haven't found any examples of how to use SRAM with microcontroller. Of course I've checked some datasheets but they are not very beginner friendly. Could anyone point me to right direction?

I'd also like to know if there are SRAMs where can be written to and read from simultaneously..? If I understand right, only one device can read from SRAM at the same time, so different devices should communicate and decide when to access ram to avoid conflict..?

You're starting off with a false premise, you don't want a micro-controller, they have internal RAM, and almost none of them can access external RAM.

If you want to build a 30 year old computer, than use 30 year old bits - Z80 or 6502 were the most popular.

And if you want to build your own video system, then buy a copy of the "Cheap Video Cookbook".

Depending what you're trying to do, you may be better off with a micro-controller and an OSD chip for your video.

 

[eblc1388]

You're starting off with a false premise, you don't want a micro-controller, they have internal RAM, and almost none of them can access external RAM.

A few AVRs, e.g. Megaa8515, Mega64, Mega128 and Mega162, can allow connection to upto 64K external SRAMs.

 

[Papabravo]

The 8051 has always supported external memory. 64K of code space and 64K of data space for a total of 128K bytes.

 

[Rasenger]

Thanks for the advices! I decided not to use SRAM - just plain microcontrollers, to keep things simple. This will limit some functionality and screen resolution, but I think I can overcome these things.

Here's my plan:

**broken link removed**

EDIT: S-Video should be Composite video.

 

[Nigel Goodwin]

The 8051 has always supported external memory. 64K of code space and 64K of data space for a total of 128K bytes.

But it never a 'real' micro-controller, more a micro-processor with pretentions!

 

[ronsimpson]

Rasenger,

Maybe you should tell us what you are really doing. By video are talking about “text” or pictures of trees and hillsides. If you want to make red and green text then this project should go one way. If you want to process broadcast video then that’s another direction.

 

[kchriste]

Here's a guy that has generated video with a low end PIC etc:
**broken link removed**
And then there is the parallax chip which is designed with video in mind:
**broken link removed**
http://www.youtube.com/watch?v=Aty0v51eo8I&feature=related