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LowresDisplayTester

What is this?

LowresDisplayTester is a small device with AVR MCUs that enables creation of low-part-count and low-cost video generator (sync generator/black burst generator/genlock) device. It also can be used as a rudimentary pattern generator, but not very stable one. Pattern generation can be disabled via a jumper on the PCB. This device also performs tests on character displays.

Features

  • Minimalistic and cheap circuitry
  • Switchable video generation standard (see list below)
  • Sync generation (composite/H+V)
  • Selectable solid fill (or black level)
  • Selectable bar pattern generation
  • Additional outputs for VFD/LED/LCD/OLED character displays
  • Compile-time configuration (via [config.h] file) to select features/firmware size

Video outputs

  • Composite RCA 525i/29.97 (NTSC no color, black level fill + white vertical bars)
  • Composite RCA 625i/25 (PAL/SECAM no color, black level fill + white vertical bars)
  • VGA 640x480 60Hz (blue fill + orange vertical bars)
  • CGA/EGA 640x200 60Hz (blue fill + cyan/magenta vertical bars)

Only one video standard can be selected at any time.

Display ports

  • HD44780-compatible (HD44780/KS0066/КБ1013ВГ6/PT6314/SPLC780/US2066/etc.) LCD/VFD/OLED character display port with 8-bit paraller data bus (used in 4-bit mode)

Firmware

Device utilizes Atmel AVR MCU for all timing, video generation and data protocols. Firmware project is done in AtmelStudio 7.

Target MCU is ATmega 168 (either variant). But firmware should be compilable and working on ATmega 328 variants as well. ATmega 48 and ATmega 88 are not supported due to low ROM capacity. ATmega 16 and ATmega 32 are also supported (but require a different PCB).

MCU must be clocked from external 16.0 MHz Xtal for precise timing.

Due to high clock and dependance of output analog levels on logic levels MCU should be run on voltages from 4.1 V to 5.0 V. Thus BOD (Brown-out Detector) is enabled by MCU fuses.

AVR fuses for ATmega328
  • SUT1 = 0
  • CKSEL3 = 0
  • SPIEN = 0
  • BODLEVEL1 = 0
  • BODLEVEL0 = 0
  • all other at "1"

In hex form:

  • low byte: 0xD7
  • high byte: 0xDF
  • extended byte: 0xFC
AVR fuses for ATmega168
  • SUT1 = 0
  • CKSEL3 = 0
  • SPIEN = 0
  • BODLEVEL1 = 0
  • BODLEVEL0 = 0
  • all other at "1"

In hex form:

  • low byte: 0xD7
  • high byte: 0xDC
  • extended byte: 0xFF
AVR fuses for ATmega16/ATmega32
  • BODLEVEL = 0
  • BODEN = 0
  • SUT1 = 0
  • SPIEN = 0
  • CKOPT = 0
  • all other at "1"

In hex form:

  • low byte: 0x1F
  • high byte: 0xCF

Hardware

Sorry, no electrical schematics at the moment.

Adapter fits onto single PCB. PCB project is done in Sprint Layout 6. Sizes of the boards:

  • LRDT.328SMD.xx (88x41 mm) for ATmega168/ATmega328 in TQFP package
  • LRDT.328DIP.xx (78x53 mm) for ATmega168/ATmega328 in DIP package
  • LRDT.32DIP.xx (78x62 mm) for ATmega16/ATmega32 in DIP package

"xx" at the end denotes revision of each PCB.

Pinout for ATmega 168/328 MCU in SMD packages

Power supply:

  • pin 4 (VCC): +5 V supply
  • pin 6 (VCC): +5 V supply
  • pin 18 (AVCC): +5 V supply (BOD)
  • pin 20 (AREF): +5 V reference
  • pin 3 (GND): 0 V (common)
  • pin 5 (GND): 0 V (common)
  • pin 21 (GND): 0 V (common)

Clock input:

  • pin 7 (PB6): 16.0 MHz Xtal
  • pin 8 (PB7): 16.0 MHz Xtal

User input:

  • pin 12 (PB0): (input) video select switch, bit 0
  • pin 16 (PB4): (input) video select switch, bit 1

Video output:

  • pin 13 (PB1): (output) composite/horizontal sync output
  • pin 32 (PD2): (input) sync input (loopback from pin 15) for additional timing
  • pin 10 (PD6): (output) vertical sync output
  • pin 14 (PB2): (output) line active part signal output
  • pin 17 (PB5): (output) bar pattern output

HD44780-compatible character display parallel port:

  • pin 1 (PD3): (output) HD44780 E (operation enable)
  • pin 9 (PD5): (output) HD44780 R/W (read/write select)
  • pin 11 (PD7): (output) HD44780 RS (command/data select)
  • pin 23 (PC0): (input/output) HD44780 D4 (data bit 4)
  • pin 24 (PC1): (input/output) HD44780 D5 (data bit 5)
  • pin 25 (PC2): (input/output) HD44780 D6 (data bit 6)
  • pin 26 (PC3): (input/output) HD44780 D7 (data bit 7)

I2C displays serial port:

  • pin 27 (PC4): (input/output) I2C data
  • pin 28 (PC5): (output) I2C clock

UART displays serial port:

  • pin 30 (PD0): (input) UART data RX from display
  • pin 31 (PD1): (output) UART data TX to display
  • pin 2 (PD4): (input) Busy signal from display
Pinout for ATmega 168/328 MCU in DIP packages

Power supply:

  • pin 7 (VCC): +5 V supply
  • pin 20 (AVCC): +5 V supply (BOD)
  • pin 21 (AREF): +5 V reference
  • pin 8 (GND): 0 V (common)
  • pin 22 (GND): 0 V (common)

Clock input:

  • pin 9 (PB6): 16.0 MHz Xtal
  • pin 10 (PB7): 16.0 MHz Xtal

User input:

  • pin 14 (PB0): (input) video select switch, bit 0
  • pin 18 (PB4): (input) video select switch, bit 1

Video output:

  • pin 15 (PB1): (output) composite/horizontal sync output
  • pin 4 (PD2): (input) sync input (loopback from pin 15) for additional timing
  • pin 12 (PD6): (output) vertical sync output
  • pin 16 (PB2): (output) line active part signal output
  • pin 19 (PB5): (output) bar pattern output

HD44780-compatible character display parallel port:

  • pin 5 (PD3): (output) HD44780 E (operation enable)
  • pin 11 (PD5): (output) HD44780 R/W (read/write select)
  • pin 13 (PD7): (output) HD44780 RS (command/data select)
  • pin 23 (PC0): (input/output) HD44780 D4 (data bit 4)
  • pin 24 (PC1): (input/output) HD44780 D5 (data bit 5)
  • pin 25 (PC2): (input/output) HD44780 D6 (data bit 6)
  • pin 26 (PC3): (input/output) HD44780 D7 (data bit 7)

I2C displays serial port:

  • pin 27 (PC4): (input/output) I2C data
  • pin 28 (PC5): (output) I2C clock

UART displays serial port:

  • pin 2 (PD0): (input) UART data RX from display
  • pin 3 (PD1): (output) UART data TX to display
  • pin 6 (PD4): (input) Busy signal from display
Pinout for ATmega 16/32 MCU in DIP packages

Power supply:

  • pin 10 (VCC): +5 V supply
  • pin 30 (AVCC): +5 V supply (BOD)
  • pin 32 (AREF): +5 V reference
  • pin 11 (GND): 0 V (common)
  • pin 31 (GND): 0 V (common)

Clock input:

  • pin 12 (XTAL2): 16.0 MHz Xtal
  • pin 13 (XTAL1): 16.0 MHz Xtal

User input:

  • pin 29 (PC7): (input) video select switch, bit 0
  • pin 28 (PC6): (input) video select switch, bit 1

Video output:

  • pin 19 (PD5): (output) composite/horizontal sync output
  • pin 16 (PD2): (input) sync input (loopback from pin 19) for additional timing
  • pin 18 (PD4): (output) line active part signal output
  • pin 20 (PD6): (output) vertical sync output
  • pin 8 (PB7): (output) bar pattern output

HD44780-compatible character display parallel port:

  • pin 35 (PA5): (output) HD44780 E (operation enable)
  • pin 34 (PA6): (output) HD44780 R/W (read/write select)
  • pin 33 (PA7): (output) HD44780 RS (command/data select)
  • pin 37 (PA3): (input/output) HD44780 D4 (data bit 4)
  • pin 38 (PA2): (input/output) HD44780 D5 (data bit 5)
  • pin 39 (PA1): (input/output) HD44780 D6 (data bit 6)
  • pin 40 (PA0): (input/output) HD44780 D7 (data bit 7)

I2C displays serial port:

  • pin 23 (PC1): (input/output) I2C data
  • pin 22 (PC0): (output) I2C clock

UART displays serial port:

  • pin 14 (PD0): (input) UART data RX from display
  • pin 15 (PD1): (output) UART data TX to display
  • pin 17 (PD3): (input) Busy signal from display

Usage

Power supply connects to the default (center-positive) DC barrel jack on the PCB. The board is equiped with reverse-polarity protection. Supplied voltage should in range of 8...20 Volts. Onboard linear volate regulator provides 5V for MCU and connected character display.

On power-on MCU starts generating video signal for selected video standard.

Note

Only one of the display output connectors should be used at any time.

Video standard is selected through "MODE" switches.

When powered MCUs also tries to communicate with a character display through HD44780 connector. Firmware has a detection procedure that tests for display presence. On detected display firmware runs a small display controller integrity test (it tests bus connection, Display RAM and CG RAM of the display). If test runs ok firmware starts character animation sequence.

Video examples and character display demos in /progress folder.

Current state

  • Two-switch video selector works
  • PAL and NTSC frame generation works ok
  • VGA, EGA and CGA frame generation works ok
  • Bar pattern for PAL/NTSC/CGA/EGA/VGA has horizontal jitter due to AVR interrupt jitter
  • HD44780 parallel (4-bit) driver works fine

Plans

  • Update I2C driver to working state
  • Write driver for character displays with I2C bus
  • Write driver for UART Futaba character displays
  • Write driver for UART terminal (?)

License

Program copyright 2022-2024.

This program is free software. Licensed under the Apache License, Version 2.0 (the "License");