v2c-firmware
Firmware for the RP2040 based Apple IIc VGA adapter
The hardware for this project is still under heavy development, and pin functions will change between board revisions. This board will NOT be usable on an Apple IIgs, as those systems have Analog RGB with a pinout incompatible with the IIc's video port.
TODO: Use the 14.318MHz pixel clock from the IIc to output VGA pixels at 28.636MHz pixel clock, with the goal of syncronizing the input and output frame rate, minimizing lag and stutter. Currently the output is clocked independant of the input, and when conflicts occur between the input DMA and CPU rendering, visual artifacts occur.
Current pin assignments as of Rev0 prototypes:
0 LED 0
1 LED 1
2 LED 2
3 LED 3
4 IIc 14.318MHz
5 IIc GR
6 IIc Sync
7 IIc Video Serial Data
8 IIc SEGB
9 IIc LDPS
10 IIc D7
11 IIc WNDW
12 Mode Button
13 Select Button
14 Reserved
15 Reserved
16 VGA B 3
17 VGA B 2
18 VGA B 1
19 VGA B 0
20 VGA G 3
21 VGA G 2
22 VGA G 1
23 VGA G 0
24 VGA R 3
25 VGA R 2
26 VGA R 1
27 VGA R 0
28 VGA H-Sync
29 VGA V-Sync
Rev1 Prototypes are slated to have the following pinout:
0 LED 0
1 LED 1
2 LED 2
3 LED 3
4 IIc 14.318MHz
5 IIc Video Serial Data
6 IIc D7
7 IIc Sync
8 IIc PRAS
9 IIc SEGB
10 IIc LDPS
11 IIc WNDW
12 IIc GR
13 IIc TEXT
14 Mode Button
15 Select Button
16 VGA B 0
17 VGA B 1
18 VGA B 2
19 VGA B 3
20 VGA G 0
21 VGA G 1
22 VGA G 2
23 VGA G 3
24 VGA R 0
25 VGA R 1
26 VGA R 2
27 VGA R 3
28 VGA H-Sync
29 VGA V-Sync
At the moment the hardware design is not finalized, and has suffered due to an unstable clock circuit. I'm expecting to have production boards ready for manufacturing in early 2024. With a clip-lead harness, this board can also be used to provide slot-free VGA output to IIe and II+ systems, similar to other projects out there.