Nuts and Volts - July/August 2018

As long as you don’t have to constantly reinvent the wheel, porting code is fun. So, instead of scratch-writing a PICBASIC PRO delay routine, we’ll just reach into the PICBASIC PRO bag of tricks and use the built-in PAUSE function to port the C __delay_ms function:

;************************************************
cmd VAR BYTE
;************************************************
;* LCD_WriteCommand
;************************************************
LCD_WriteCommand:
regAddr = GPIO_A_ADDRESS
regData = $60
call LCD_WriteIOExpander
regAddr = GPIO_B_ADDRESS
regData = cmd
call LCD_WriteIOExpander
regAddr = GPIO_A_ADDRESS
regData = $20
call LCD_WriteIOExpander
return
void LCD_Initialize(void) {
 LCD_WriteIOExpander(IO_DIR_A_ADDRESS, OUTPUT_
DIR);
 LCD_WriteIOExpander(IO_DIR_B_ADDRESS, OUTPUT_
DIR);
 LCD_WriteIOExpander(GPIO_A_ADDRESS, LCD_VDD_
EN);
 __delay_ms(10);
 LCD_WriteCommand(LCD_FUNCTION_SET);
 __delay_ms(10);
 LCD_WriteCommand(LCD_SET_DISPLAY);
 __delay_ms(10);
 LCD_WriteCommand(LCD_CLEAR);
 __delay_ms(10);
 LCD_WriteCommand(LCD_SET_DISPLAY);
 __delay_ms(130);
 LCD_WriteCommand(LCD_SET_DDRAM_ADDRESS);
 __delay_ms(1);
}
 ;************************************************
 ;* LCD CONSTANTS
 ;************************************************
 LCD_CLEAR CON $01
 LCD_VDD_EN CON $20
 LCD_FUNCTION_SET CON $3C
 LCD_SET_DISPLAY CON $0C
 LCD_SET_DDRAM_ADDRESS CON $80
 LINE1_START_ADDRESS CON $80
 LINE2_START_ADDRESS CON $C0
 OUTPUT_DIR CON $00
 ;************************************************
 ;* LCD_Initialize
 ;************************************************
 LCD_Initialize:
 regAddr = IO_DIR_A_ADDRESS
 regData = OUTPUT_DIR
 call LCD_WriteIOExpander
 regAddr = IO_DIR_B_ADDRESS
 regData = OUTPUT_DIR
 call LCD_WriteIOExpander
 regAddr = GPIO_A_ADDRESS
 regData = LCD_VDD_EN
 call LCD_WriteIOExpander
 pause 10
 cmd = LCD_FUNCTION_SET
 call LCD_WriteCommand
 pause 10
 cmd = LCD_SET_DISPLAY
 call LCD_WriteCommand
 pause 10
 cmd = LCD_CLEAR
 call LCD_WriteCommand
 pause 10
 cmd = LCD_SET_DISPLAY
 call LCD_WriteCommand
 pause 130
 cmd = LCD_SET_DDRAM_ADDRESS
 call LCD_WriteCommand
 pause 1
 return

As we continue to add to our base of LCD driver functions, the easier the porting becomes. The LCD initialize C function is based on the LCD_WriteIOExpander and LCD_WriteCommand functions:

#define LCD_CLEAR 0x01
#define LCD_VDD_EN 0x20
#define LCD_FUNCTION_SET 0x3C
#define LCD_SET_DISPLAY 0x0C
#define LCD_SET_DDRAM_ADDRESS 0x80
#define LINE1_START_ADDRESS 0x80
#define LINE2_START_ADDRESS 0xC0
#define OUTPUT_DIR 0x00

The LCD is now under our control. All that’s left to do is port the C source that writes human-readable stuff to the display. There are four C functions we need to port. The first function writes a single byte to the LCD via the MCP23S17: