October 27, 2021

Explore Forth on the Expandable Planck 6502 Computer Running at 12 MHz

from hackster.io

For many reasons, the venerable 6502 microprocessor continues to be the centerpiece of 8-bit single board computers (SBCs). One such project is the Planck 6502 Computer.

The project's designer, Jonathan Foucher, is a software engineer who designs hardware for personal use and then shares it. Here is what he says about Planck 6502.

"You can use the computer from this kit standalone by connecting it to your computer with a USB to serial adapter, or you can add up to six extension boards to make it function as a standalone computer." — Jonathan Foucher, Planck 6502 designer.

The motherboard contains the CPU, RAM, ROM, and six expansion slots. The CPU is a modern 65c02 running at 12 MHz. That clock speed is roughly ten times faster than the first computers that used a 6502 from MOS Technology back in the 1980s.

Tail Forth 2 is the primary software interface to the computer. This modern version of Forth is explicitly designed for the 65c02 and SBCs like Planck 6502. Fortunately, since the onboard 32 kilobyte EEPROM stores the code, you can easily replace Tail Forth 2 with something else. For example, you could port over a version of BASIC or develop a monitor program.

The six expansion slots extend Planck 6502 with boards like an input/output adapter, character LCD driver, video graphics array (VGA), and many others. One exciting-sounding board contains a Yamaha YM3812 FM synthesizer chip. This chip was also known as the OPL2 and was very popular on IBM-compatible sound cards like the Adlib and Sound Blaster.

On the I/O board, there are interfaces like a PS/2 keyboard, parallel port, and a bus called 65SIB. That bus is a serial interface defined by the users on the 6502.org forum. It is similar to and compatible with the SPI (and Quad SPI) protocol found on modern devices.

Even with all the pre-designed options, do not fret if Foucher does not have the card design that you need or want. There are KiCad design files available to get you started on creating your own expansion board.

Foucher has made the design files and firmware available on the Planck 6502 Computer Gitlab repo.