361 Multi Segment Monitor
361 : Multi Segment Monitor
- Author: Matt Venn & Claude
- Description: Simulates a 64x37 array of 7 segment displays on a VGA screen
- GitHub repository
- Open in 3D viewer
- Open in Tiny Tapeout Explorer
- Open in VGA Playground
- Clock: 40000000 Hz
How it works
Simulates a wall of 7 segment displays on a VGA screen: a 64 x 37 grid of digits — 2368 digits, 18944 segments, each segment with its own 4 bit brightness, sent through a colour palette on the way out. Video is 800x600 @ 60 Hz from a 40 MHz clock.
There is no framebuffer. The chip races the beam and keeps only the digit row being drawn, in a 1 kB SRAM buffer holding four rows of 256 bytes. Each segment is the AND of an x zone and a y zone within its 12x16 cell.
uio[7] selects the data source:
- Internal generator (low): a slowly varying zone plate, no external data needed. The palette changes itself every 1024 frames (~17 s), fading through black.
- Stream port (high): a byte on
ui_inis latched on the rising edge of the strobe onuio[6]. Byte n of a frame is digit n/4, nibble pair n%4; 256 bytes per row, 9472 per frame, nibbles in the order a, b, c, d, e, f, g, DP. The write pointer resets on vsync, so a lost or extra byte costs one frame and then corrects.
A digit row is 16 scanlines and 256 bytes, so a host sending one byte every 66 pixel clocks tracks the raster exactly. The first byte must follow vsync within about 450 µs.
Reset strap
ui_in[3:0] is sampled while rst_n is low (the last value before it rises sticks):
| Bit | Meaning |
|---|---|
ui_in[0] |
0 = Digilent PmodVGA, 1 = Tiny Tapeout VGA Pmod |
ui_in[3:1] |
palette: 0 grey, 1 blue, 2 green, 3 purple, 4 amber, 5 red, 6 cyan, 7 fire |
DIP switches
Can be changed in generator mode only. All off is the default attract mode.
| Bit | Off | On |
|---|---|---|
ui_in[3:1] |
starting palette | palette held in manual mode |
ui_in[4] |
palette cycles | hold the palette ui_in[3:1] names |
ui_in[5] |
ring speed wanders | steady ring speed |
ui_in[6] |
drift speed wanders | steady drift |
Config packet
With uio[7] low, strobes on uio[6] carry config bytes. Each fall of uio[7] starts
a packet. The first valid header also stops the DIP switches being read.
| Byte | Contents |
|---|---|
| 0 | {4'hA, load_preset, cycle_en, 0, pmod_type}; without the A the packet is ignored |
| 1–3 | red curve: {knee_x, knee_y}, m1, m2 (slopes in eighths, 5 bits) |
| 4–6 | green, the same |
| 7–9 | blue, the same |
A palette is three per-channel curves, each two lines through a knee, clipped at 15. A
header alone changes the Pmod or turns preset cycling on or off; load_preset restores
the strapped preset. tools/palette_builder designs curves and exports the bytes.
How to test
Generator. Leave uio[7] low, apply a 40 MHz clock and release reset. Concentric
rings should flow across the grid, with the palette changing every ~17 s. Each DIP
switch should change what you see within two frames.
Streaming. Set uio[7] high and push 9472 bytes per frame on ui_in, restarting on
each vsync. tools/video2seg.py converts a video or image to that format and
firmware/seg_player.py streams it from the demoboard's RP2350 over PIO and DMA.
Edit seg_player.py to set the Pmod type and palette choice.
External hardware
Digilent PmodVGA across both output headers: R and B nibbles on uo_out, G nibble
plus hsync and vsync on uio[5:0], 4 bits per channel. Strobe and mode select use
uio[7:6], which PmodVGA leaves unconnected.
Tiny Tapeout VGA Pmod: strap ui_in[0] high; video moves onto uo_out at 2 bits
per channel and uio[5:0] become inputs.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | stream data 0 / reset strap: 0=Digilent PmodVGA, 1=Tiny VGA Pmod | Digilent: R0 / Tiny VGA: R1 | Digilent: G0 (unused, Tiny VGA) |
| 1 | stream data 1 / strap+switch: palette bit 0 | Digilent: R1 / Tiny VGA: G1 | Digilent: G1 (unused, Tiny VGA) |
| 2 | stream data 2 / strap+switch: palette bit 1 | Digilent: R2 / Tiny VGA: B1 | Digilent: G2 (unused, Tiny VGA) |
| 3 | stream data 3 / strap+switch: palette bit 2 | Digilent: R3 / Tiny VGA: vsync | Digilent: G3 (unused, Tiny VGA) |
| 4 | stream data 4 / switch: 1 = hold palette ui[3:1], 0 = change every 512 frames | Digilent: B0 / Tiny VGA: R0 | Digilent: hsync (unused, Tiny VGA) |
| 5 | stream data 5 / switch: 1 = steady ring speed, 0 = let it wander | Digilent: B1 / Tiny VGA: G0 | Digilent: vsync (unused, Tiny VGA) |
| 6 | stream data 6 / switch: 1 = steady source drift, 0 = let it wander | Digilent: B2 / Tiny VGA: B0 | stream strobe; config strobe while uio[7] is low (same pin in both Pmod modes) |
| 7 | stream data 7 | Digilent: B3 / Tiny VGA: hsync | 1 = stream data, 0 = internal generator + config packets (same pin in both Pmod modes) |