847 UART VGA Text Scroller
847 : UART VGA Text Scroller
- Author: Noble G
- Description: Receives a text message over UART and scrolls it across a 640x480 VGA display.
- GitHub repository
- Open in 3D viewer
- Open in Tiny Tapeout Explorer
- Open in VGA Playground
- Clock: 25175000 Hz
UART VGA Text Scroller with 2-bit ALU
Overview
This Tiny Tapeout design contains two independent blocks:
- A UART-controlled 640 × 480 VGA scrolling-text display.
- A 2-bit combinational ALU on the bidirectional pins.
The VGA block receives up to 32 characters at 9600 baud, stores the message internally, renders a 5 × 7 font at 4× scale, and scrolls the text continuously from right to left. Text colour, background colour, scroll speed, and pause are selectable through ui_in[7:0].
The ALU is purely combinational and operates independently of the VGA/UART logic.
VGA / UART Features
- 640 × 480 VGA
- 9600 baud, 8-N-1 UART
- Maximum 32-character message
- 5 × 7 font scaled 4×
- 32 × 32 pixel character cell
- Four scroll speeds
- Pause/resume
- Four text colours
- Four background colours
- Lowercase converted to uppercase
- CR or LF restarts scrolling
Dedicated Inputs
| Pin | Function |
|---|---|
ui_in[0] |
Scroll speed bit 0 |
ui_in[1] |
Scroll speed bit 1 |
ui_in[2] |
Pause scrolling |
ui_in[3] |
UART RX |
ui_in[4] |
Text colour bit 0 |
ui_in[5] |
Text colour bit 1 |
ui_in[6] |
Background colour bit 0 |
ui_in[7] |
Background colour bit 1 |
Scroll Speed
ui_in[1:0] |
Speed |
|---|---|
00 |
1 pixel/frame |
01 |
2 pixels/frame |
10 |
4 pixels/frame |
11 |
8 pixels/frame |
Text Colour
ui_in[5:4] |
Colour |
|---|---|
00 |
White |
01 |
Yellow |
10 |
Cyan |
11 |
Magenta |
Background Colour
ui_in[7:6] |
Colour |
|---|---|
00 |
Black |
01 |
Dark blue |
10 |
Dark green |
11 |
Dark red |
VGA Outputs
| Pin | VGA signal |
|---|---|
uo_out[0] |
R1 |
uo_out[1] |
G1 |
uo_out[2] |
B1 |
uo_out[3] |
VSYNC |
uo_out[4] |
R0 |
uo_out[5] |
G0 |
uo_out[6] |
B0 |
uo_out[7] |
HSYNC |
2-bit Combinational ALU
Pin allocation
| Pin | Direction | Signal |
|---|---|---|
uio[0] |
Input | A[0] |
uio[1] |
Input | A[1] |
uio[2] |
Input | B[0] |
uio[3] |
Input | B[1] |
uio[4] |
Input | SEL[0] |
uio[5] |
Input | SEL[1] |
uio[6] |
Output | Y[0] |
uio[7] |
Output | Y[1] |
Thus:
A = uio[1:0]
B = uio[3:2]
SEL = uio[5:4]
Y = uio[7:6]
The bidirectional output-enable value is:
uio_oe = 11000000
so uio[5:0] are inputs and uio[7:6] are outputs.
ALU functions
SEL[1:0] |
Operation | Expression |
|---|---|---|
00 |
Addition | Y = A + B |
01 |
Subtraction | Y = A - B |
10 |
Bitwise AND | Y = A & B |
11 |
Bitwise XOR | Y = A ^ B |
The ALU result is two bits wide. Addition and subtraction therefore operate modulo 4.
Example:
A = 11 (3)
B = 10 (2)
SEL = 00
3 + 2 = 5
2-bit Y = 01
Supported Characters
- A–Z
- 0–9
- Space
.-!?:
Clock
The VGA/UART block is designed for approximately 25.175 MHz.
The ALU is combinational and does not require the clock.
Tiny Tapeout Configuration
- Top module:
tt_um_nobleg30_uart_vga_scroller - HDL: Verilog
- Tile size: 1 × 2
- Clock: 25.175 MHz
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | Scroll speed bit 0 | VGA R1 | |
| 1 | Scroll speed bit 1 | VGA G1 | |
| 2 | Pause scrolling | VGA B1 | |
| 3 | UART RX | VGA VSYNC | |
| 4 | Text colour bit 0 | VGA R0 | |
| 5 | Text colour bit 1 | VGA G0 | |
| 6 | Background colour bit 0 | VGA B0 | |
| 7 | Background colour bit 1 | VGA HSYNC |