AVR PCD8544 DRIVER DOCUMENTATION

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1 AVR PCD8544 DRIVER DOCUMENTATION Ishraq Ibne Ashraf 14th September

2 1. INTRODUCTION AVR PCD8544 Driver is a one header file driver for supporting AVR microcontrollers in driving PCD8544 based 84x48 dot-matrix displays. Compared to all the Arduino based drivers this driver is quite low level. The users will have convenience making character sets or doing low level stuffs with the display. This driver provides the independence to choose various megaavr MCUs and does not depend on specific a board like Arduino. 2. DEPENDENCIES There are some dependencies of this driver noted as follows, Currently this driver only supports megaavrs. The AVR for which the driver is being used must have hardware SPI support. Only hardware SPI with SPCR, SPSR and SPDR registers is supported by this driver. 3. FEATURES Below are the features of this driver, Simple and easy interface for controlling the PCD8455 based 84x48 dot-matrix displays. Does not depend on specific board like Arduino but supports most of the megaavrs. Being quite low level gives the freedom to design new custom electronics with megaavrs and PCD8544 based displays. Provides convenience to develop new character sets and custom graphics. The user doesn't have to worry about the initialization of the display. It is done by calling a function which is available on the interface. Custom commands can be set from the functions of the interface. Function available on the interface to write data and any command to the display controller. 4. USAGE Its quite simple using this driver. Below is a step by step description of how to use this driver, 1. Add the header file in the project in which the driver needs to be installed. 2. Include the header file on the file of the project where the driver must be used. 3. There are some mandatory preprocessor defines that must be defined before the include of the header file. These defines are described on TABLE After the previous steps the interface functions can be used and accessed in the project. 2

3 5. THE INTERFACE 5.1 HARDWARE The serial communication interface of the PCD8544 controller uses the following lines, SCE PIN DESCRIPTION This is the CHIP select pin of the controller. Active LOW. DC This pin of the controller defines where the received data is a command or data. 0 = COMMAND, 1 = DATA. RES MOSI MISO SCLK BL 5.2 MANDATORY DEFINES This is the reset pin of the controller. Active LOW. Serial data out pin of the controller. Which is connected to the serial data in pin of the display controller. Serial data in pin of the controller. SPI clock pin of the controller. This pin is connected to the serial clock pin of the display controller. Back-light controller pin. This pin is connected to the backlight pin of the display controller. TABLE-5.1 These defines are to define the interface used to communicate with the display controller. With these defines six pins are defined those are used. Each pin has three defines for defining the DDR, PORT and the pin number in the port that is being used. Lets say we are using pin number 2 of PORTB as our SCE pin. In this case the defines for the SCE pin should be as following, #define SCE_DDR DDRB #define SCE_PORT PORTB #define SCE_PIN 2 LISTING-5.2 Below is TABLE-5.2 that describes all these mandatory defines. 3

4 #define SCE_DDR <DDR_REGISTER> #define SCE_PORT <PORT_REGISTER> #define SCE_PIN <PIN_NUMBER> #define DC_DDR <DDR_REGISTER> #define DC_PORT <PORT_REGISTER> #define DC_PIN <PIN_NUMBER> #define RES_DDR <DDR_REGISTER> #define RES_PORT <PORT_REGISTER> #define RES_PIN <PIN_NUMBER> #define MOSI_DDR <DDR_REGISTER> #define MOSI_PORT <PORT_REGISTER> #define MOSI_PIN <PIN_NUMBER> #define MISO_DDR <DDR_REGISTER> #define MISO_PORT <PORT_REGISTER> #define MISO_PIN <PIN_NUMBER> #define SCLK_DDR <DDR_REGISTER> #define SCLK_PORT <PORT_REGISTER> #define SCLK_PIN <PIN_NUMBER> #define BL_DDR <DDR_REGISTER> #define BL_PORT <PORT_REGISTER> #define BL_PIN <PIN_NUMBER> SCE PIN DEFINES DC PIN DEFINES RES PIN DEFINES MOSI PIN DEFINES MISO PIN DEFINES SCLK PIN DEFINES BL PIN DEFINES TABLE-5.2 4

5 5.3 FUNCTIONS The function set provided by this driver is divided into four types, 1. General Functions 2. Function Set 3. Basic Instructions 4. Extended Instructions The functions which take arguments from the user during invocation returns 0 for failure and 1 for success after executing the function. Its best if the user is always checks for these return values during invocation of these functions. The tables below describes the functions of this driver interface GENERAL FUNCTIONS FUNCTION NAME RETURNS ARGUMENTS DESCRIPTION pcd8544_init void void Initialize the display controller. pcd8544_send_command uint8_t : 0 or 1 [1]uint8_t : Command to be sent pcd8544_write_data uint8_t : 0 or 1 [1]uint8_t : Data to be written Send commands to the controller in byte. Send data to be written to the display in byte. pcd8544_clear_screen void void Clears all the pixels of the display. pcd8544_fill_screen void void Turns on all the pixels of the display. pcd8544_backlight_toggle uint8_t : 0 or 1 [1] uint8_t : Turn BL on/off (0 = OFF, 1 = ON) TABLE Turns the display backlight on/off. 5

6 5.3.2 FUNCTION SET FUNCTION NAME RETURNS ARGUMENTS DESCRIPTION pcd8544_cmd_function_set uint8_t : 0 or 1 [1]uint8_t : PD(Power Down) [2]uint8_t : V(Vertical or Horizontal Addressing) [3]uint8_t : H(Basic or extended instructions) BASIC INSTRUCTIONS TABLE Controls the parameters defined as function set on the pcd8544 datasheet. FUNCTION NAME RETURNS ARGUMENTS DESCRIPTION pcd8544_cmd_nop void void Sends NOP instruction to the display contorller pcd8544_cmd_display_blank void void Blanks the display. pcd8544_cmd_normal_mode void void Switches to normal mode. pcd8544_cmd_all_segments _on pcd8544_cmd_inverse_video _mode void void Turns on all segments. void void Enables inverse video mode. pcd8544_cmd_setx uint8_t : 0 or 1 [1]uint8_t : The X coordinate (0-83) pcd8544_cmd_sety uint8_t : 0 or 1 [1]uint8_t : The Y coordinate (0-5) pcd8544_cmd_setxy uint8_t [1]uint8_t : The X coordinate (0-83) [2]uint8_t : The Y coordinate (0-5) Sets X coordinate of the cursor on the display. Sets Y coordinate of the cursor on the display. Sets the X and Y coordinate of the cursor. pcd8544_cmd_setxy_origin void void Sets X and Y coordinates of the cursor at zero EXTENDED INSTRUCTIONS TABLE FUNCTION NAME RETURNS ARGUMENTS pcd8544_cmd_set_temp erature_coefficient pcd8544_cmd_set_bias_ system uint8_t : 0 or 1 uint8_t : 0 or 1 [1]uint8_t : Temperature coefficient value (0-3) [1]uint8_t : Bias system value (0-7) pcd8544_cmd_set_vop uint8_t : 0 or 1 [1]uint8_t : Operating voltage value (0-63) TABLE DESCRIPTION Sets the temperature coefficient. Sets the bias system. Sets the operating voltage. 6

7 6. EXAMPLE CODE SNIPPET //defines for SCE pin #define SCE_DDR DDRB #define SCE_PORT PORTB #define SCE_PIN 2 //defines for DC pin #define DC_DDR DDRB #define DC_PORT PORTB #define DC_PIN 0 //defines for RES pin #define RES_DDR DDRB #define RES_PORT PORTB #define RES_PIN 1 //defines for MOSI pin #define MOSI_DDR DDRB #define MOSI_PORT PORTB #define MOSI_PIN 3 //defines for MISO pin #define MISO_DDR DDRB #define MISO_PORT PORTB #define MISO_PIN 4 //defines for SCLK pin #define SCLK_DDR DDRB #define SCLK_PORT PORTB #define SCLK_PIN 5 //defines for BL pin #define BL_DDR DDRD #define BL_PORT PORTD #define BL_PIN 7 //program includes #include <avr/io.h> #include "avr_pcd8544_driver.h" #include "util/delay.h" //the main function int main(){ //initializing the display pcd8544_init(); //turning on the display backlight pcd8544_backlight_toggle(0x01); while(1){ } //turning on all the pixels of the screen pcd8544_fill_screen(); _delay_ms(250); //turning off all the pixels of the screen pcd8544_clear_screen(); _delay_ms(250); } return 0; LISTING-6 7

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