This LIB can use several different models of PCF8574 based I2C to LCD interfaces
The most important difference between such modules is whether they use P0~P3 or
P4~P7 for the 4 bit data nibble to the LCD. This LIB can ONLY deal with LO or HI nibbles.
If the data bits are spread across the PCF8574 port bits in other ways,
then the user will have to edit the code in SUB LCDI2C_DirectSend

The most important call is LCDI2C_Init which configures the library appropriately.
LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo

Where I2CAddr is the I2C Address
NibPos=0 use low 4 bits ie P0~P3, NibPos=1 use high 4 bits ie P4~P7
RSBitNo is PCF8574 bit number for RS 0~7
ENBitNo is PCF8574 bit number for EN 0~7
BLBitNo is PCF8574 bit number for Backlight control 0~7


Using the I2C -> LCD Interface from eBay priced about US$1.60
http://www.ebay.co.uk/itm/291116790762?ssPageName=STRK:MEWNX :IT&_trksid=p3984.m1439.l2649
http://www.youtube.com/watch?v=wmTWk4Rwfw0

Uses PCF8574 - 8 bit I2C Port Expander
I2CAddress is &H27 with unjumpered address pads
PCF8574 port is wired as follows
P0 - RS
P1 - RW
P2 - EN
P3 - Backlight On/Off
P4 - D4 LCD
P5 - D5 LCD
P6 - D6 LCD
P7 - D7 LCD

LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
LCDI2C_Init &H27,1,0,2,3


Using BigMik board (see http://www.thebackshed.com/forum/forum_posts.asp?TID=6715&PN =1&TPN=2)
Uses PCF8574 - 8 bit I2C Port Expander
I2CAddress is &H20~&H27 depending on jumper settings
PCF8574 port is wired as follows
P0 - D4
P1 - D5
P2 - D6
P3 - D7
P4 - RS
P5 - RW ?
P6 - Backlight ?
P7 - EN

LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
LCDI2CInit &H2X,0,4,7,6

'Test suite for LCDI2CLib

'Initialise the I2C LCD device
'LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
LCDI2C_Init &H27,1,0,2,3
WaitForAKey("Press any key for next test")

'Turn On the Backlight
LCDI2C_BacklightOn
WaitForAKey("Press any key for next test")

'Turn OFF the Backlight
LCDI2C_BacklightOff
WaitForAKey("Press any key for next test")

'Turn On the Backlight
LCDI2C_BacklightOn
WaitForAKey("Press any key for next test")

LCDI2C 1,3,DATE$
WaitForAKey("Press any key for next test")

LCDI2C 2,4,TIME$
WaitForAKey("Press any key for next test")

LCDI2C_Clear
WaitForAKey("Press any key for next test")

DO

' L=TIMER 'DEBUG
LCDI2C 1,3,DATE$
LCDI2C 2,4,TIME$
' PRINT TIMER-L 'DEBUG

LOOP

END

SUB WaitForAKey(Msg$)
IF Msg$="" THEN Msg$="Press any key to continue"
PRINT Msg$;
DO
LOOP WHILE INKEY$=""
PRINT
END SUB

'----------------------------------------------------------- -------
'
' LCDI2CLib V2 2014-July-09
'
' Micromite to LCD using I2C module
'
' (c) Peter Carnegie 2014
'
' This code is a heavily modified version of I2CLCD.BAS by John Gerrard
'
' This LIB can use several different models of PCF8574 based I2C to LCD interfaces
' The most important difference between such modules is whether they use P0~P3 or
' P4~P7 for the 4 bit data nibble to the LCD. This LIB can ONLY deal with LO or HI nibbles. If the
' data bits are spread across the PCF8574 port bits in other ways, then the user will
' have to edit the code in SUB LCDI2C_DirectSend
'
' The most important call is LCDI2C_Init which configures the library appropriately.
' LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
'
' Where I2CAddr is the I2C Address
' NibPos=0 use low 4 bits ie P0~P3, NibPos=1 use high 4 bits ie P4~P7
' RSBitNo is PCF8574 bit number for RS 0~7
' ENBitNo is PCF8574 bit number for EN 0~7
' BLBitNo is PCF8574 bit number for Backlight control 0~7
'
'
' Using the I2C -> LCD Interface from eBay priced about US$1.60
' http://www.ebay.co.uk/itm/291116790762?ssPageName=STRK:MEWNX :IT&_trksid=p3984.m1439.l2649
' http://www.youtube.com/watch?v=wmTWk4Rwfw0
'
' Uses PCF8574 - 8 bit I2C Port Expander
' I2CAddress is &H27 with unjumpered address pads
' PCF8574 port is wired as follows
' P0 - RS
' P1 - RW
' P2 - EN
' P3 - Backlight On/Off
' P4 - D4 LCD
' P5 - D5 LCD
' P6 - D6 LCD
' P7 - D7 LCD
'
' LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
' LCDI2C_Init &H27,1,0,2,3

'
' Using BigMik board (see http://www.thebackshed.com/forum/forum_posts.asp?TID=6715&PN =1&TPN=2)
' Uses PCF8574 - 8 bit I2C Port Expander
' I2CAddress is &H20~&H27 depending on jumper settings
' PCF8574 port is wired as follows
' P0 - D4
' P1 - D5
' P2 - D6
' P3 - D7
' P4 - RS
' P5 - RW ?
' P6 - Backlight ?
' P7 - EN
'
' LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo
' LCDI2CInit &H2X,0,4,7,6

' Functions in the Library are modelled after the native MMBasic LCD commands
' to ease code conversion
'
' Sub LCDI2C(LineNum,CharPos,Text$) Display string Text$ on LineNum of the display starting at CharPos
' Sub LCDI2C_Clear() Clears the LCD
' LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo Initialise the I2C and LCD
' Sub LCDI2C_Close() Close the I2C LCD

' SUB LCDI2C_BacklightOn() Turn LCD backlight ON
' SUB LCDI2C_BacklightOff() Turn LCD backlight OFF

' SUB LCDI2C_CMD(Byte) Send a COMMAND byte to the LCD, ie RS=0
' SUB LCDI2C_DATA(Byte) Send a DATA byte to the LCD, ie RS=1
'
' SUB LCDI2C_DirectSend(Byte) Send a BYTE to the LCD - used internally by the lib
' SUB LCDI2C_WireWrite(Byte) Write a byte onto the I2C bus to the LCD
'
'
' Uses 6 Global Variables
' LCDI2C_LCDBackLight, LCDI2C_I2CAddr, LCDI2C_RSDataMask,
' LCDI2C_EMask, LCDI2C_BackLight, LCDI2C_NibPos
'



'----------------------------------------------------------- -------
'
' Print String to LCD
'
'
SUB LCDI2C(LineNum,CharPos,Text$)
LOCAL I
IF LineNum=1 THEN I=(&H80 + CharPos-1)
IF LineNum=2 THEN I=(&HC0 + CharPos-1)
LCDI2C_CMD(I)

FOR I=1 TO LEN(Text$)
LCDI2C_DATA(ASC(MID$(Text$,I,1)))
NEXT I

END SUB


'----------------------------------------------------------- -------
'
' Clear LCD
'
'
SUB LCDI2C_Clear()
LCDI2C_CMD(&H01)
END SUB


'----------------------------------------------------------- -------
'
' INITIALIZE LCD
'
'
SUB LCDI2C_Init I2CAddr,NibPos,RSBitNo,ENBitNo,BLBitNo

'Backlight Control bit
DIM LCDI2C_BackLight
LCDI2C_BackLight=2^BLBitNo

'Current Backlight state - default to ON
DIM LCDI2C_LCDBackLight
LCDI2C_LCDBackLight=LCDI2C_BackLight

'I2C Bus Address
DIM LCDI2C_I2CAddr
LCDI2C_I2CAddr=I2CAddr

'RS Control bit
DIM LCDI2C_RSDataMask
LCDI2C_RSDataMask=2^RSBitNo

'EN Control Bit
DIM LCDI2C_EMask
LCDI2C_EMask=2^ENBitNo

'Save if P0~P3 or P4~P7 bits of PCF8574 port
DIM LCDI2C_NibPos
LCDI2C_NibPos=NiBPos

'Start I2C
I2C OPEN 400,100

'%0011---- %0011---- 8-bit / 8-bit
LCDI2C_CMD(&H33)
'%0011---- %0010---- 8-bit / 4-bit
LCDI2C_CMD(&H32)

' Byte commands - To configure the LCD

' Display Format
' 4bit mode, 2 lines, 5x7
'
' 001LNF00
' %00101000
LCDI2C_CMD(&H28)

' L : 0 = 4-bit Mode 1 = 8-bit Mode
' N : 0 = 1 Line 1 = 2 Lines
' F : 0 = 5x7 Pixels 1 = N/A


' Setup Display
' Display ON, Cursor On, Cursor Steady
'
' 00001DCB
' %00001110
LCDI2C_CMD(&H0C)

' D : 0 = Display Off 1 = Display On
' C : 0 = Cursor Off 1 = Cursor On
' B : 0 = Cursor Steady 1 = Cursor Flash


' Setup Cursor/Display
' Inc Cursor Cursor Move
'
' 000001IS
LCDI2C_CMD(&H06)
' I : 0 = Dec Cursor 1 = Inc Cursor
' S : 0 = Cursor Move 1 = Display Shift

LCDI2C_CMD(&H01)

'Turn Off LCDBacklight
LCDI2C_BackLightOff()

END SUB


'----------------------------------------------------------- -------
'
' Close the I2C LCD
'
'
SUB LCDI2C_Close()

'Close the I2C Bus
I2C CLOSE

END SUB


'----------------------------------------------------------- -------
'
' Turn Backlight On
'
'
SUB LCDI2C_BacklightOn
LCDI2C_LCDBacklight=LCDI2C_Backlight
LCDI2C_WireWrite(0)
END SUB


'----------------------------------------------------------- -------
'
' Turn Backlight Off
'
'
SUB LCDI2C_BacklightOff
LCDI2C_LCDBackLight=&H00
LCDI2C_WireWrite(0)
END SUB


'----------------------------------------------------------- -------
'
' Send Command Byte to LCD
'
'
SUB LCDI2C_CMD(Byte)

'Send Hi Nibble
LCDI2C_DirectSend(Byte AND &HF0)

'Send Low Nibble
LCDI2C_DirectSend((Byte AND &H0F) * 16)

END SUB


'----------------------------------------------------------- -------
'
' Send Data Byte to LCD
'
'
SUB LCDI2C_DATA(Byte)

'Send Hi Nibble
LCDI2C_DirectSend((Byte AND &HF0) OR LCDI2C_RSDataMask)

'Send Lo Nibble
LCDI2C_DirectSend(((Byte AND &H0F) * 16) OR LCDI2C_RSDataMask)

END SUB


'----------------------------------------------------------- -------
'
' Send Byte to LCD over I2C
' NB, we don't call LCDI2C_WireWrite in this SUB because that results in
' MUCH slower execution time than inlin'ing the I2C Write's
'
'
SUB LCDI2C_DirectSend(Byte)

LOCAL B,B1

'Use a copy so that we don't mess up caller's argument

'IS D4-D7 of LCD mapped to P0~P3 of PCD8574 ?
IF LCDI2C_NibPos=0 THEN
B1=Byte\16
ELSE
B1=Byte
ENDIF

'Take EN high, use B 'cos it's quicker than doing the OR's in the I2C Write command itself
B=B1 OR LCDI2C_EMask OR LCDI2C_LCDBacklight
I2C WRITE LCDI2C_I2CAddr,0,1,B

'Take EN Low
I2C WRITE LCDI2C_I2CAddr,0,1,B1 OR LCDI2C_LCDBacklight

END SUB


'----------------------------------------------------------- -------
'
' Send Byte over I2C
'
'
SUB LCDI2C_WireWrite(Byte)
I2C WRITE LCDI2C_I2CAddr,0,1,Byte OR LCDI2C_LCDBacklight
END SUB