reDIP CIA

MOS 6520 PIA / MOS 6522 VIA / MOS 6526/8520/8521 CIA FPGA replacement

Overview

The reDIP CIA is an open source FPGA board which combines the following in a DIP-40 size package:

• Lattice iCE5LP1K FPGA
• 1Mbit FLASH
• 5V tolerant I/O

The reDIP CIA provides an open source hardware platform for MOS 6520 PIA / MOS 6522 VIA / MOS 6526/8520/8521 CIA replacements.

Designs for the iCE5LP1K FPGA can be processed by yosys and nextpnr.

I/O interfaces

DIP-40 header pins:

• 5V input
• 35 FPGA GPIO
• 3 FPGA open-drain I/O
• GND

All FPGA header I/O is 5V tolerant, and can drive 5V TTL.

SPI / programming header:

A separate header footprint is provided for (Q)SPI flash programming, with pinout borrowed from the iCEBreaker Bitsy.

MOS 6526/8521 and MOS 8520 CIA compatibility

The board is fully pin compatible with the venerable MOS 6526/8521 and MOS 8520 CIA chips.

Cycle accurate emulation of the MOS 6526/8521 and MOS 8520 CIA chips has been implemented in gateware, configurable via software.

MOS 6522 VIA compatibility

Cycle accurate emulation of the MOS 6522 VIA chip has been implemented in gateware. Please note that this is currently completely untested!

MOS 6520 PIA compatibility

Cycle accurate emulation of the MOS 6520 VIA chip has been implemented in gateware. Please note that this is currently completely untested!

Thanks

The gateware implementations would not have been possible without the outstanding work on varius MOS chips by Frank "androSID" Wolf and Dieter "ttlworks" Müller.