This example demonstrates the generation of an analogue VGA signal from a PIC32 microcontroller using general output pins. It follows on from the work done in the VGAPIC32 project. The result is not entirely satisfactory:
It might be possible to introduce some kind of delay and even out the pixel widths, but this has not been investigated with hardware. However, unlike the vga-pmp example, there is no accompanying signal to potentially orchestrate the staging of individual pixels at a slightly delayed rate. Potentially, the peripheral clock signal might be generated and processed to make such a signal.
Unlike the vga example, this example employs two DMA channels for pixel data which are interleaved to investigate a potential remedy for the wide pixel effect. Unfortunately, despite each channel contributing every other word (or group of four pixels), the effect persists. However, the picture is perhaps more stable than in the vga example.
One significant problem with this example is that scrolling causes the DMA channels to become ordered incorrectly. This does not affect the vga-timer example which also employs two DMA channels.
The pin usage of this solution is documented below.
MCLR# 1 \/ 28 HSYNC/OC1/RA0 2 27 VSYNC/OC2/RA1 3 26 RB15/U1TX D0/RB0 4 25 RB14 D1/RB1 5 24 RB13/U1RX D2/RB2 6 23 D3/RB3 7 22 RB11/PGEC2 8 21 RB10/PGED2 RA2 9 20 RA3 10 19 D4/RB4 11 18 RB9 12 17 RB8 13 16 RB7/D7 D5/RB5 14 15
Note that RB6 is not available on pin 15 on this device (it is needed for VBUS unlike the MX170 variant).
UART1 is exposed by the RB13 and RB15 pins.
For one bit of intensity, two bits per colour channel:
D7 -> 2200R -> I I -> diode -> R I -> diode -> G I -> diode -> B D6 (not connected) D5 -> 470R -> R D4 -> 1000R -> R D3 -> 470R -> G D2 -> 1000R -> G D1 -> 470R -> B D0 -> 1000R -> B HSYNC -> HS VSYNC -> VS