Файл: Basic for PIC Microcontrollers (M. Nebojsa, 2001).pdf

4.24 I2CWRITE Writing data to I2C peripheral device

Description: I2WRITE sends control and address data via I2C interface. We define 8-bit or 16-bit address while defining variable put to address parameter (in order to correctly define address size, we must have accurate information on device we are communicating with).

If peripheral device is serial EEPROM, it is necessary to wait for 10ms (depending on device) until writing has ended. New communication with device is possible after 10ms have elapsed. If new data write occurs before the last one has ended, request will be ignored. Address size is either 1 or 2 bytes, depending on device connected. A problem may occur when trying to write multiple bytes in one instruction, depending on specific EEPROM. Such instances can be avoided if, instead of EEPROM, we use devices without the need for pause between writing. If 2-byte data (WORD) is sent, higher byte goes first, then the lower. For string transfer, STR goes before the name of the string, and number of clocks after \ .

a var byte[8]

I2CWRITE PORTC.4, PORTC.3, $a0, 0, [STR a\8]

If optional label is used, program will jump onto the label if there is no response signal over the I2C interface. Standard transfer rate (100kHz) is achieved by 8MHz oscillator. For higher transfer rate (400kHz) 20MHz oscillator is used. If slower oscillator is used for the transfer program should contain the following directive:

DEFINE I2C_SLOW 1

In order to have bipolar I2C clock interface and not an open collector, following DEFINE directive should be used:

DEFINE I2C_SCLOUT

Operating any peripheral units with I2C communication requires that you study the supplier manual and specifications.

4.25 INPUT Designates I/O pin as input

4.26 IF-THEN-ELSE Conditional program branching

Description: Instruction selects one of two possible program paths. Instruction IF is the fundamental instruction of program branching in PIC BASIC and it can be used in several ways to allow

flexibility necessary for realization of decision making logic.

The simplest form of instruction is shown on the picture above. Sample program below tests the button connected to RB0 - when the button is pressed program jumps onto the label “Add” where value of variable “w” is increased. If the button is not pressed, program jumps back onto the label “Main”.

Example:

w var byte

Main :

IF PORTB.0=0 THEN Add goto Main

Add : W=W+1

End

More complex form of instruction is program branching with the ELSE part of instruction.

w var byte Main :

IF PORTB.0=0 THEN Add

ELSE Subtract

ENDIF

goto Main Add : W=W+1 Subtract : W=W-1

End

Same effect can be achieved directly :

w var byte

Main :

IF PORTB.0=0 THEN W=W+1

ELSE W=W-1

ENDIF

goto Main

End

4.27 LCDOUT Prints data on LCD display

Description: LCDOUT sends the data to the LCD (Liquid Crystal Display). PIC BASIC supports various LCD models which have Hitachi 44780 controller or compatible one. LCD usually has either 14 or 16 pins for connection to a microcontroller. If there is character # before data, ASCII value of every data is sent to LCD. LCDOUT has the same modifiers as the instruction SEROUT2.

Before the first instruction is sent to LCD, program should wait for at least half a second for LCD to initialize.

LCD display can be connected to PIC microcontrollers by either 4-bit or 8-bit bus. If 8-bit bus is used, all of 8 bits mus t be connected to the same port, while in the case of 4-bit bus all 4 bits must be either in the upper or the lower part of byte. R/W line should be connected to ground if LCD is used only for data display. PIC BASIC assumes that LCD is connected to specific pins if DEFINE directives do not say otherwise. Default is 4-bit bus with lines DB4-DB7 connected to RA0-RA3, RS pin connected to RA4 and E pin connected to RB 3. Also, it is assumed that LCD is 2x16. For changing any of the default settings, appropriate DEFINE directives can be used.

If LCD is connected to some other microcontroller lines it has to be defined with DEFINE directives, as shown in the following example.

DEFINE LCD_COMMANDS 2000 ‘ command delay in microseconds

Definitions above define 2-line LCD on 4 -bit bus on the upper 4 bits of microcont roller port D. Register Select (RS pin) is on PORTD.2 and Enable is on PORTD.3.

Every LCD controller is in charge of certain commands. Commands are sent by instruction: LCDOUT $FE, $Kod. List of commands is shown in table below.

4.28 LCDIN Reads data from LCD RAM