HI2C Overview


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.


Up to 100 kbit/s.

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


Up to 1 Mbit/s.

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

Not Supported

Up to 3.4 Mbit/s.

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

Not Supported

Relevant Constants:

These constants control the setup of the hardware I2C methods:

Constant Controls Usage


Operational mode of the microcontroller

HI2CMode ( Master )


Operational mode of the microcontroller

HI2CMode ( Slave )


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

#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.

Port Settings:

The settings of the pin direction is critical to the operation of these methods. Both pins must be set as inputs and be pulled up with an appropriate resistor (typically 4.k @ 5.0v for 100Mkz transmissions).

Constant Controls Default Value


Pin on microcontroller connected to I2C data

Must be defined


Pin on microcontroller connected to I2C clock)

Must be defined


This example examines the IC2 devices and displays on a serial terminal. This code will require adaption but the code shows an approach to discover the IC2 devices.

    ' Hardware I2C Overview - using the ChipIno board, see
    ' http://www.elproducts.com/chipino.html for information

    #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

    HI2CMode Master

    #define USART_BAUD_RATE 9600
    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
      HI2CSend ( deviceID )

      if HI2CAckPollState = false then

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

      end if

    HSerPrint   "End of Device Search"
    HSerPrintCRLF 2

Supported in <HI2C.H>