Single-Wire Serial LCD Terminal

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This is designed to use a serial terminal is 16 characters × 1 line LCD display Module HD44780 basis.
It is used to control display and PIC16F628A With the host computer communication. In the serial transmitter and receiver built into the informed consent to allow two-way communication With any of the RS — 232 devices. This parameter has been set to 9600 baud, 8 bits, No parity, one stop bit.

Circuit diagram below. 7805 a three-terminal regulator to step down The supply is greater than any available down to about 8V, stability requires 5 volts Display module. Display module itself is connected to a write-only device, the R / W type Main Line direct connection to ground.

Display Module B covers an area of ​​six lines In PIC, the other two lines dedicated to the serial interface. The implementation of the two transistors The necessary level shifting between the inversion and the prior informed consent and RS — 232 level. Port A is completely free of charge, visit here for connecting a keyboard or similar input device available.

Five lines This port is available. If you do not need to reset the device pin can be configured as 4 acts As input. Therefore, the four normal I / O lines, one of the open-drain output (RA4) and a progressive And the only input device (RA5 / MCLR) is used for other purposes.
Informed consent within the plan is reproduced below. It has been assembled into a hex file using MPLAB Free from Microchip. Characters being received through the serial port in a round eight-deep buffer saved. The display is When cleared, print linefeed or return character is received.

This takes time, during this period Up to three or four characters may be accepted. Whenever a character is received, a flag is set. This gets reset by the buffer empty. Circular buffer is implemented using two eight-mode is always up-counter. These counters are incremented each time phase 7.

This sets the zero order, so that the count Always range from zero to seven, eight or die. Received a receipt for counter increments Character and received the position at the counter of characters stored in the buffer. When a new character display, display counter increments and the characters in the Location in the buffer to be sent to the display.

Then, the two counters are compared. If they are equal, all Has received the character display, so the «new word can be» signs be reset. Since the display uses a single chip HD44780 is 16 characters for each of two eight. This requires daily control of the character display position tracking and the necessary control The word appears in the correct position the ninth characters.

Sixteen characters have been sent to the Ignore any further conventional module printable characters.

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