HI2C Overview

Introduction:

These methods allow Great Cow BASIC programs to send and receive Inter- Integrated Circuit (I2C™) messages via:

  • Master Synchronous Serial Port (MSSP) module of the microcontroller for the Microchip PIC architecture, or
  • ATMEL 2-wire Serial Interface (TWI) for the Atmel AVR microcontroller architecture.

These methods are serial interfaces that are useful for communicating with other peripheral or microcontroller devices. These peripheral devices may be serial EEPROMs, shift registers, display drivers, A/D converters, etc.

The method can operate in one of two operational modes:

  • Master Mode, or
  • Slave mode (with general address call)

These methods fully implement all the I2C master and slave functions (including general call support) and supports interrupts on start and stop bits in hardware to determine a free bus (multi-master function).

These methods implement the standard mode specifications as well as 7-bit and 10-bit addressing. A “glitch” filter is built into the SCL and SDA pins when the pin is an input. This filter operates in both the 100 KHz and 400 KHz modes. In the 100 KHz mode, when these pins are an output, there is a slew rate control of the pin that is independent of device frequency.

A hardware I2C/TWI module within the microcontroller is required for these methods.

The driver supports two hardware I2C ports. The second port is addressed by the suffix HI2C2. All HI2C commands are applicable to the second HI2C2 port.

The method supports the following frequencies:

Frequency Description Support

Up to 400 kbits/s

I2C/TWI fast mode: Defined as transfer rates up to 400 kbit/s.

Supported

Up to 100 kbit/s.

I2C/TWI standard mode: Defined as transfer rates up to 100 kbit/s.

Supported

Up to 1 Mbit/s.

I2C fast-mode plus: Allowing up to 1 Mbit/s.

Supported on I2C Module Only

Requires alternative clock source to be set.

Up to 3.4 Mbit/s.

I2C high speed: Allowing up to 3.4 Mbit/s.

Supported on I2C Module Only

Requires alternative clock source to be set.

Relevant Constants:

These constants control the setup of the hardware I2C methods:

Constant Controls Usage

Master

Operational mode of the microcontroller

HI2CMode ( Master )

Slave

Operational mode of the microcontroller

HI2CMode ( Slave )

HI2C_BAUD_RATE

Operational speed of the microcontroller. Defaults to 100 kbit/s

For Microchip SSP or MSSP modules and AVR microcontrollers:

#define HI2C_BAUD_RATE 400 or
#define HI2C_BAUD_RATE 100.
Where #define HI2C_BAUD_RATE 100 is the default value and therefore does need to be specified.

For Microchip I2C module:

'define HI2C_BAUD_RATE 125' is the default. You can override this value if you set up an alternative clock source.

HI2CITSCLWaitPeriod

Sets the TSCL period to Zero as the Stop condition must be held for TSCL after Stop transition. Default to 70, some solutions can use this set to 0. The clock source and clock method must be reviewed before changing this setting.

#define HI2CITSCLWaitPeriod 70

Port Settings:

The settings of the pin direction is critical to the operation of these methods.
For the Microchip SSP/MSSP modules both ports must be set as input.
For the Microchip I2C module bith ports must be set as output. And, configure the pins as open-drain and set the I2C levels - see example below for usage.
In all case the data and clock line *must * be pulled up with an appropriate resistor (typically 4.k @ 5.0v for 100Mkz transmissions).

Constant Controls Default Value

HI2C_DATA

Pin on microcontroller connected to I2C data

Must be defined

HI2C_CLOCK

Pin on microcontroller connected to I2C clock)

Must be defined


Microchip I2C modules Specific Support

Clock Sources: The Microchip I2C can select one of ten clocks sources as shown in the table below. I2C1Clock_MFINTOSC is the default which support 125hz.
To change the clock source, change the constant as follows:

        #define I2C1ClockSource  I2C1Clock_MFINTOSC

Clock Constants

Constant Clock Source Default Value

I2C1Clock_SMT1

SMT

0x09

I2C1Clock_Timer6PSO

Timer 6 Postscaler

0x08

I2C1Clock_Timer4PSO

Timer 4 Postscaler

0x07

I2C1Clock_Timer2PSO

Timer 2 Postscaler

0x06

I2C1Clock_Timer0Overflow

Timer 0 Overflow

0x05

I2C1Clock_ReferenceOut

Reference clock out

0x04

I2C1Clock_MFINTOSC

MFINTOSC

0x03 (default)

I2C1Clock_HFINTOSC

HFINTOSC

0x02

I2C1Clock_FOSC

FOSC

0x01

I2C1Clock_FOSC4

FOSC/4

0x00



Alternative Clock Source: Using SMTClock source as the clock spurce, the following methods implement the SMT as the clock source. The defintion of the constant, the include, setting of the SMT period, initialisation and starting of the clock source are ALL required.

    #define I2C1ClockSource I2C1Clock_SMT1
    #Include <SMT_Timers.h>

    '400 KHZ @ 64MHZ
    SETSMT1PERIOD ( 39 )
      ' 100 KHZ @ 64MHZ
      ' SETSMT1PERIOD ( 158 )
    InitSMT1(SMT_FOSC,SMTPres_1)
    StartSMT1

For other clock sources refer to the appropriate datasheet.

Error Codes: This module has extensive error reporting. For the standard error report refer to the appropriate datasheet. Great Cow BASIC also exposes the following error messages to enable the user code to handle the errors appropriately. These are exposed via the variable HI2C1lastError - the bits of the HI2C1lastError are set as in the table shown below.

Constant Error Value/Bit

I2C1_GOOD

0

I2C1_FAIL_TIMEOUT

1

I2C1_TXBE_TIMEOUT

2

I2C1_START_TIMEOUT

4

I2C1_RESTART_TIMEOUT

8

I2C1_RXBF_TIMEOUT

16

I2C1_ACK_TIMEOUT

32

I2C1_MDR_TIMEOUT

64

I2C1_STOP_TIMEOUT

128


Shown below are two examples of using Hardware I2C with Great Cow BASIC.


Example 1:
This example examines the IC2 modules using the Microchip SSP/MSSP module and the AVR microcontrollers. This will display the result on a serial terminal. This code will require adaption but the code shows an approach to discover the IC2 devices.

    #chip mega328p, 16
    #config MCLRE_ON

    ' Define I2C settings
    #define HI2C_BAUD_RATE 400
    #define HI2C_DATA PORTC.5
    #define HI2C_CLOCK PORTC.4
    'I2C pins need to be input for SSP module when used on Microchip PIC device
    Dir HI2C_DATA in
    Dir HI2C_CLOCK in

    'MASTER MODE
    HI2CMode Master

    'USART/SERIAL PORT WORKS WITH max232 THEN TO PC Terminal
    #define USART_BAUD_RATE 9600
    #define USART_TX_BLOCKING
    Dir PORTc.6 Out
    #define USART_DELAY 10 ms

    HSerPrintCRLF 2
    HSerPrint "Hardware I2C Discover using the "
    HSerPrint CHipNameStr
    HSerPrintCRLF 2

    for deviceID = 0 to 255
      HI2CStart
      HI2CSend ( deviceID )

      if HI2CAckPollState = false then

         if (( deviceID & 1 ) = 0 ) then
         HSerPrint "W"
        else
         HSerPrint "R"
        end if
        HSerSend 9
        HSerPrint   "ID: 0x"
        HSerPrint   hex(deviceID)
        HSerSend 9
        HSerPrint "(d)"+str(deviceID)
        HSerPrintCRLF
        HI2CSend ( 0 )

      end if

      HI2CStop
    next
    HSerPrintCRLF
    HSerPrint   "End of Device Search"
    HSerPrintCRLF 2



This example examines the IC2 devices and displays on a serial terminal for the I2C module only.
This code will require adaption but the code shows an approach to discover the IC2 devices.
This code will only operate on the Microchip I2C module.

    #chip 18f25k42, 16
    #option Explicit
    #config mclr=on, LVP=on

    #startup InitPPS, 85

    Sub InitPPS

          RC4PPS =      0x22   'RC4->I2C1:SDA1
          RC3PPS =      0x21   'RC3->I2C1:SCL1
          I2C1SCLPPS =  0x13   'RC3->I2C1:SCL1
          I2C1SDAPPS =  0x14   'RC4->I2C1:SDA1

          'Module: UART1
          RC6PPS = 0x0013     'TX1 > RC6
          U1RXPPS = 0x0017    'RC7 > RX1

    End Sub

    'Template comment at the end of the config file

    'Setup Serial port
    #define USART_BAUD_RATE 9600
    #define USART_TX_BLOCKING


    ' Define I2C settings
    #define HI2C_BAUD_RATE 125
    #define HI2C_DATA PORTC.4
    #define HI2C_CLOCK PORTC.3
    'Initialise I2C - note for the I2C module the ports need to be set to Output.
    Dir HI2C_DATA out
    Dir HI2C_CLOCK out
    RC3I2C.TH0=1   'Port specific controls may be required - see the datasheet
    RC4I2C.TH0=1   'Port specific controls may be required - see the datasheet

    'For this solution we can set the TSCL period to Zero as the Stop condition must be held for TSCL after Stop transition
    #define HI2CITSCLWaitPeriod 0

    '*****************************************************************************************************
    'Main program commences here.. everything before this is setup for the board.

    dim DeviceID as byte
    Dim DISPLAYNEWLINE as Byte

     do

        HSerPrintCRLF
        HSerPrint "Hardware I2C "
        HSerPrintCRLF 2

          ' Now assumes Serial Terminal is operational
          HSerPrintCRLF
          HSerPrint "   "
          'Create a horizontal row of numbers
          for DeviceID = 0 to 15
            HSerPrint hex(deviceID)
            HSerPrint " "
          next

          'Create a vertical column of numbers
          for DeviceID = 0 to 255
            DisplayNewLine = DeviceID % 16
            if DisplayNewLine = 0 Then
              HSerPrintCRLF
              HserPrint hex(DeviceID)
              if DisplayNewLine > 0 then
                HSerPrint " "
              end if
            end if
            HSerPrint " "

            'Do an initial Start
            HI2CStart
            if HI2CWaitMSSPTimeout <> True then

              'Send to address to device
              HI2CSend ( deviceID )

              'Did device fail to respond?
              if HI2CAckPollState = false then
                HI2CSend ( 0 )
                HSerPrint   hex(deviceID)
              Else
                HSerPrint "--"
              end if
              'Do a stop.
              HI2CStop

            Else
              HSerPrint "! "
            end if

          next

          HSerPrintCRLF 2
          HSerPrint   "End of Search"
          HSerPrintCRLF 2
          wait 1 s
          wait while SwitchIn = On
      loop



Supported in <HI2C.H>