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On this page, I will introduce the electronic signboard with PIC16F84A.
The message is displayed to flow on the left from the right.
128 LEDs are used for this board.

In the software of this equipment, following techniques are used.

Indirect addressing memory
The indirect addressing method is the way of doing the reading/the writing from/to the memory by setting the address of the memory to the FSR register. When using this method, the access address of the memory can be calculated by addition or subtracting and the processing of access to the continued memory is possible to do easily.
Access to the EEPROM memory

The data which was memorized at the EEPROM memory doesn't disappear even if the power is switched off.
Because the PIC16F84A has 64 byres EEPROM memory, the messages for a maximum of 64 bytes can be set.
The data which is used with this equipment are not a character form. Each bit shows the lighting-up(0)/the going-out(1) of the LED.
Timer interrupt

It is possible to process periodically with the hardware timer. While the hardware timer is counting time, the software can do the other processing.
In the software, the scroll of the message is periodically done by the interruption processing of hardware timer. And the lighting-up control processing of LEDs is executed in the waiting time of scroll.

Processor Frequency10MHz
LEDHigh brightness LED x 128
The message scroll time ( 26msec x n ) /1 row
n =< 256
The message quantityA maximum of 64 bytes (Bit pattern)
The message patternOne kind

Circuit drawing

Pattern drawing

Circuit explanation

Parts explanation

Flow chart


Processing explanation