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.
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, or even use Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for MakeCode, CircuitPython, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.
Have an amazing project to share? The Electronics Show and Tell with Google Hangouts On-Air is every Wednesday at 7:30pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.
