SALE TODAY! 15% off! Use the code BLACKFRIDAY15 on checkout *some restrictions apply.

December 7, 2011 AT 11:08 am

Veronica – ROM Emulator

Img 0942

Follow up to previous post! Veronica – ROM Emulator @ Blondihacks. Quinn writes –

If you recall from last time, we got Veronica to perform a free run by NOP-ing her way through a phantom memory space.

Well, the next logical step is to get some real memory for her to run code from. I’m calling this a ROM Emulator, because it’s faking what would be the role of Read-Only Memory in a normal CPU startup sequence. The code and data will be entered into this memory by an external tool, and the CPU will not be able to write to it. In all other ways, however, it looks like regular memory to our girl.

A RAM chip by itself can’t do a whole lot. When powered up, it will be full of random junk. We need a method of data entry. Early computers usually had a big bank of toggle switches and blinking lights to handle this. If you’ve seen an old Altair or an old PDP-8, you know what I’m talking about. Hollywood has made sure we will always think Important Computers look like that. Anyways, the point of those switches and lights is to modify RAM directly, in order to give the CPU code to run immediately upon startup. It’s another one of those chicken-and-egg problems that plagued early computers. The CPU needs code in memory to run, but the CPU is usually what loads code into memory. You need a way to bootstrap that cycle.

Check out all the Circuit Playground Episodes! Our new kid’s show and subscribe!

Have an amazing project to share? Join the SHOW-AND-TELL every Wednesday night at 7:30pm ET on Google+ Hangouts.

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Learn resistor values with Mho’s Resistance or get the best electronics calculator for engineers “Circuit Playground”Adafruit’s Apps!

Maker Business — Thank you from Adafruit

Wearables — Need a lot of power for your project? Read on!

Electronics — Watch the gate voltage!

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at !

No Comments

No comments yet.

Sorry, the comment form is closed at this time.