The ATtiny4313 terminal project is a modification to the ATtiny2313 project. No PCB mods are required, but three resistors need to be left off.
ATtiny2313 PC board, schematics, and source code
Attiny4313 Schematics, and source code

ATtiny4313 Serial Terminal with LCD and PS/2 Keyboard

The ATtiny2313 terminal was a success in that it was a magnitude better than the ATmega8 version in reliability, being less of a wiring puzzle and more of a finished product, but there were some misses, too:

• There is no way to change the backlight color without taking the thing apart
• The contrast adjustment was a waste of code, since there is only one "right" value
• The settings had to be reentered on reset or power up

To make these improvements, I started another project that would allow more parameters to be changed via keyboard, by entering a configuration mode, changing the parameters, and saving them to EEPROM on return to terminal mode. It would have more flash, so the parameters could be changed via a configuration screen. One hurdle I encountered was the end of the 2k flash. I had to switch to the ATtiny4313, which was expected, since I was 2 bytes from the end with the ATtiny2313 terminal firmware.

Parameters that may be changed and stored in the ATtiny EEPROM are:

• Color
• Intensity
• Quiet mode
• Character translation for non-printable characters
• Serial Baud rates:
  • 300
  • 1200
  • 2400
  • 4800
  • 9600
  • 19.2k
  • 38.4k
  • 57.6k
  • 76.8k
  • 115.2k (with 14.7456 MHz crystal)
  • 230.4k (with 14.7456 MHz crystal)

When the terminal boots it displays a message on the LCD display, and sends that message to the serial port. For some applications this might be a bad thing. Quiet mode suppresses that message on the serial port.

These connectors are all mounted on one edge of the PC board, so when it is held vertically, the cables will all come out the bottom of the box:

• 2.5mm power jack
• 4-pin mini-din for serial
• 6-pin mini-din for the keyboard

The contrast pot is also located there. There is a power LED that indicates the power is properly applied for troubleshooting when the display is dark. If the LED is on and the LCD is off, you have a code or hardware problem in the color or brightness sections.

ATtiny4313 serial terminal schematic

The area outlined in the schematic is the circuitry that is on the small transistor board. In the final ATtiny4313 board, the entire circuit will be on one board.

Parts List for the ATtiny4313 Serial Terminal

The parts list for the terminal. Prices are Mouser.com unless indicated:

• 763-0216K1Z-NS-FBWR1 LCD display $14.75
• 556-ATTINY4313-PU ATtiny4313 microcontroller $2.80
• 161-2304 Circular DIN Connectors MINI DIN PCB 4 PIN for serial $1.31
• 161-2306 Circular DIN Connectors MINI DIN PCB 6 PIN for keyboard $1.52
• 571-6-535541-6 (2 ea) AMPMODU 18-pin female header $2.01 each
• 942-IRF7470TRPBF IR SO-8 HEXFET $1.68
• 512-FDS6975 (2 ea) Fairchild SO-8 Dual P-channel MOSFET $1.23 each
• PC board - made by Futurlec $25.00 setup + $4.00 per board

Junk box parts:

• 20-pin socket
• 7805
• Either a PS/2 keyboard or a USB keyboard with PS/2 adapter
• Various resistors and capacitors
• Crystal 14.7456 MHz or 16 MHz (only serial baud rate divisor is affected by the frequency)

Assembly

Bottom side of board

The three resistors used to set the current in the LED backlight are removed, and the transistor board is wired into their places. In addition, the drive signals from PORTD 4:6 are wired to the board. The normal contrast circuit is removed entirely. There are not enough pins on an ATtiny4313 to do both RGB and contrast. The contrast pot is used instead.

Transistor board

Configuration

The firmware defaults to 1/2 brightness white, 19.2kBaud, not quiet, and translates control characters to hex. To change any of that, press the "menu" key to enter configuration mode. The current values for all options are displayed. The following keys will then select the parameter to configure:

• r = Select red brightness value
• g = Select green brightness value
• b = Select blue brightness value
• i = Select intensity value
• q = Select quiet mode value
• t = Select control character translation value
• s = Select serial Baud rate

The cursor will go to the parameter chosen, and you can then use the up and down arrows to adjust the value. The color brightness can be adjusted in the range of 0 (off) to 3 (full on). The intensity can be adjusted from 0 to 15. Quiet mode prevents the terminal from sending the banner message to the serial port, in case that might interfere with the operation of the board you are talking to. Control character translation converts the characters sent from the board to the terminal, should they fall outside the printable ASCII range. Press "menu" again to leave configuration mode. Any data received on the serial port during configuration will be discarded. When you leave configuration mode the changes will be written to EEPROM.

The ATtiny4313 serial terminal set to a red backlight

The ATtiny4313 serial terminal set to a green backlight (the camera doesn't do it justice)

The ATtiny4313 serial terminal set to a blue backlight

If you are going to change the range of the colors or brightness, you may need to change the frequency of timer0 so that it doesn't "beat" with the display refresh and cause a noisy background. Red, green, blue, magenta, cyan, and yellow all look really good. The camera can't reproduce the colors properly. They are very distinct colors. The green is greener than any green LED I've ever seen.