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PART 2: Emulator and EPROM Basics
by George Martin

Start ı Making The Choice ı Getting The Debugger Going ı Putting It All Together ı Sources and PDF

GETTING THE DEBUGGER GOING

I set up the debugger by plugging the EPROM emulator into the EPROM socket and attaching it to my PC using a serial or parallel cable. Loading code from powerup is a two-step process. First, I load the PDREM software into the EPROM Emulator and then my application. Once the PDREM software is loaded, I can just keep changing and reloading my application code as long as the application controls the CPU. If my CPU locks up or spins off into never-never land, I need to reload both the PDREM and the application.

With PDREM support, I can look at assembly language and single step the CPU, as well as keep an eye on the memory and I/O. In fact, I can even operate at the C source level, monitoring variables and stepping through complete C source statements. All in all, itıs quite powerful.

EPROM SELECTION

Although I described how this EPROM emulator connects, I skipped over the EPROM Iım emulating. Even though EPROMs come in all sorts of sizes and shapes, I typically think of them as the devices programmed and then erased using UV light. However, now that the ICıs features are so small, UV light is no longer practical. In fact, many EPROMs are one-time programmable (OTP).

I also need to consider flash-memory devices for my EPROM. Flash is erasable and reprogrammable, even while itıs in the circuit. The PC BIOS has used flash-memory technology for several years now.

As I sort through the devices, packaging again becomes one of the definitive parameters. EPROMs are available in a dual-inline package (DIP) of up to 32 pins. Although the package is large, itıs easy to work with.

Its size is limited, though. The largest Iıve found is only 8-bit devices with a 512K x 8 memory configuration. If you want a larger EPROM or a wider data path, then you have to use two devices in parallel or switch to a surface-mount package (SMT). If you use SMT, then 16-bit data paths and 2M x 16 flash-memory devices are readily available.

EPROM emulators come with connectors that plug into DIP sockets. Depending on the device I select, Iıll need adapters to make the connection. Also, the 8-bit interface is standard, and if I use wider data paths, Iıll need additional EPROM emulators connected in parallel. While all this is possible, it adds a whole lot of complexity to development, so Iıll opt for the easier route.

For this project, Iıve selected the 512K x 8 flash-memory device as my EPROM, and Iıll get it in a DIP package.

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