[Bradley] decided to tackle the challenge to recreate the original Nintendo Entertainment System’s processor in a Field Programmable Gate Array. Say what? The original NES is a Legacy System, still used but no longer manufactured. If a system breaks, it becomes more and more difficult to repair or find replacements parts as time passes. By using a programmable integrated circuit such as a CPLD or a FPGA to clone the functionality of the original hardware, legacy systems can live on long after the original hardware has given up the ghost.

It took [Bradley] about a year to fully implement the NES processor as part of his Master’s project at Bradley University. He used what was known about the processor combined with some detective work with logic probes along the way. The programming was done in VHDL and those files are available for download (click on Documentation).

With the ubiquity of NES emulators on every device known to man you probably won’t be replicating this unless you want a reason to play with a FPGA. What interests us is the hardware solution this type of work provides for obsolete hardware that still serves a useful purpose. If you’ve used a FPGA or similar device to keep an old system running, let us know about it in the comments.

In our Dev Phone 1 excitement last week, we somehow overlooked phoneWreck’s teardown of the T-Mobile G1. The complex slider mechanism is certainly worth looking out. One of the major oddities they point out is the inclusion of two vibration motors. One is mounted next to the SIM on the mainboard. While the other is mounted in the frame next to the earpiece. We wonder what was gained/solved by using two. The phone also includes a digital compass module. We’d like a more detailed explanation of how the Xilinx CPLD is used. From this article in 2006, it seems HTC uses them to generate custom clock signals and switching off devices for power management.

Complex programmable logic devices (CPLDs) contain the building blocks for hundreds of 7400-serries logic ICs. Complete circuits can be designed on a PC and then uploaded to a CPLD for instant implementation. A microcontroller connected to a CPLD is like a microcontroller paired with a reprogrammable circuit board and a fully stocked electronics store.

At first we weren’t sure of the wide appeal and application of CPLDs in hobbyist projects, but we’ve been convinced. A custom logic device can eliminate days of reading datasheets, finding the ideal logic IC combination, and then waiting for chips to arrive. Circuit boards are simpler with CPLDs because a single chip with programmable pin placement can replace 100s of individual logic ICs. Circuit mistakes can be corrected by uploading a new design, rather than etching and stuffing a new circuit board. CPLDs are fast, with reaction times starting at 100MHz. Despite their extreme versatility, CPLDs are a mature technology with chips starting at $1.

We’ve got a home-etchable, self programming development board to get you started. Don’t worry, this board has a serial port interface for working with the CPLD, and doesn’t require a separate (usually parallel port) JTAG programmer.

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