2.3 KiB
apple-one
This is a very untested and very basic implementation of an Apple 1 in a iCE40HX FPGA. It has enough to run Woz Mon via the serial USB interface which is available on the iCE40HX8K-B-EVN breakout board, which makes this a very compact little set up.
I've also wired up support for a LED&KEYS IO board using my TM1638 verilog module.
This project borrows heavily from the work of Andrew Holme and his "Pool" project where he built a 6502 CPU core in Verilog using the netlist from the Visual 6502 project. Amazing stuff, and so far seems to work perfectly.
As it stands this project uses the following resources in the iCE40HX8K
Total Logic Cells: 1739/7680
Combinational Logic Cells: 634 out of 7680 (8.25%)
Sequential Logic Cells: 1105 out of 7680 (14.38%)
Logic Tiles: 295 out of 960 (30.72%)
Registers:
Logic Registers: 1105 out of 7680 (14.38%)
IO Registers: 0 out of 1280 (0%)
Block RAMS: 16 out of 32 (50%)
Global Buffers: 6 out of 8 (75%)
PLLs: 0 out of 2 (0%)
##Memory Map
The memory is as basic as basic can be. 50% of the iCE40HX8K is used currently, but this gives the Apple 1 basically 8K of memory which is plenty to start with.
The Zero page and Stack page is covered, and a small 256 byte "ROM" is positioned up at 0xFF00 -> 0xFFFF.
| Start | End | Description |
|---|---|---|
| 0x0000 | 0x1FFF | 8KB of block RAM. 0x1F00 -> 0x1FFF is the "ROM" data. |
| 0xD000 | Output register for the breakout LEDs | |
| 0xD010 | UART RX register used by Woz Mon | |
| 0xD011 | UART RX control register. Woz Mon checks the MSB for received flag | |
| 0xD012 | UART TX register and control. The TX register only writes 7 bits to the remote host. The MSB is read by Woz Mon to confirm the UART isn't busy sending | |
| 0xD020 | LED&KEYs display register. [4] is display on/off, [3:0] is brightness | |
| 0xD021 | 0xD028 | LED&KEYs digit data for digit 1 to 8 |
| 0xD029 | LED&KEYs LEDs 1 to 8 | |
| 0xD030 | LED&KEys input register for the buttons 1 to 8. [7] is button 1, [0] is button 8 | |
| 0xFF00 | 0xFFFF | Woz Mon pointed to by the RESET vector |