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RB6502






What is RB6502?

RB6502 is a piece of hardware based on the Godil, meant to replace the original 6502.


The hardware

The Godil is placed on a piece of experiment board using two 50-pins headers. At the bottom I soldered an obselete 40-pins DIL IC. The core of this IC has been bored out to avoid clashes with its hardware.

To be able to monitor the signals, I added a 50-pins SCSI header. A flat cable enables me to connect it a old Escom laptop. The laptop is placed on a small docking station which has room for one ISA card. In this case a card with 96 I/O lines. 48 of them are connected to the Godil. The other two provide power and ground. The power enables to program and to test the Godil even when it is not placed on a 6502 computer.


The core

The core is written in VHDL. It is written by my self for two reasons:
- I could have used T65 or the core of the 1541Ultimate as base, but I didn't understand both of them.
- I wanted to learn VHDL in the hard way.
I started to understand both cores but I still don't understand the base of the design. I based my VHDL core on the way I want to build my TTL 6502. So far the core works fine (only simulation for the moment) but it has on disadvantage for the moment: it uses about twice as much resources of the FPGA as T65 and the core of the Ultimate. Why? I haven't any idea yet.





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