Dot Matrix Display

Warning! Danger! Alert!
This was my first serious PIC project, and PICs were the first microcontrollers I laid my hands upon.
This project is old, poor and generally obsolete. Please do not look at it. Thank you.

Look at this instead.

Obsolete page begins here

LED Dot Matrix Display (done!)

Using PIC16F84 microcontroller and 11 other logic ICs

As promised, it's ready for Asm'2k!

The hardware consists of six LED matrix modules (5x7) and 13 ICs:

1 x PIC16F84-10/P
1 x SN74LS273N
1 x SN74LS245N
3 x HCF4093BE
6 x HCF4017BE
1 x LM317T

The software consists of:

The firmware code in the PIC. About 300 words long and uses all 68 bytes of the controller RAM. No EEPROM used.
The PC software that drives the display through the parallel printer port. Up to 4 displays on a single port would be possible.

Some pictures of the prototype I built for ASM'99:

(With two of the LED modules removed)

matrix2.jpg (58702 bytes)

matrix1.jpg (65348 bytes)

Schematics...

Schematics are also available as OrCAD 9 Project file (.opj) here (30k). Those with no OrCAD can use the big GIF images.

Get the MCU assembler source file here.

Get the C source code for the driver software (bare bones, just enough to make it work) here. For BC++ 3.1 (DOS), may also compile with DJGPP, but it's not tested.

Get the mtxfont.dat here, the file that contains the FULL ASCII font (chars 0-255) in binary format. This is the font that's shown on the display.

FYI, here's the protocol:

The PIC RAM is implemented as double-buffered framebuffer. 30 bytes is used for each page.
Each bit of a byte in the framebuffer represents a LED.
The least significant bits in the framebuffer are unused.
The image displayed on the "screen" is software-rendered from font data on disk. Graphics are possible.
The software (a TSR hooked to the timer interrupt or RTC interrupt) sends 30 bytes for each frame.
Each byte is sent:
- By setting the data valid on the LPT port data bus.
- Pulsing the Strobe pin (long enough for the PIC to catch it)
- Holding data valid until the PIC has processed the interrupt
- Note that the MSB of the PC data is unused, the PIC shifts data left by 1.
The last byte of each frame has a "1" in the MSB, which informs the PIC to flip a page.
Displays narrower than 30 columns can be implemented with this protocol.

That's it. The data valid time depends on the port speed to which the display is connected to. For more info, email me.

Using PIC16F84 microcontroller and 11 other logic ICs

As promised, it's ready for Asm'2k!

Some pictures of the prototype I built for ASM'99:

Schematics...

Last updated: October 5, 2000. Content copyright (C) Antti Koskipää 2000. All trademarks acknowledged.