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AN #142 - Using MAX1668 with BASCOM-AVR Print
Connecting the MAX1668 to the AT90S2313 by Roland van Leusden

The MAX1668 is a precise multichannel digital thermometer that report the temperature of 4 remote sensors and it's own package. The remote sensors are diode-connected transistors—typically low-cost, easily mounted 2N3904 NPN types—that replace conventional thermistors or thermocouples. The remote channels can also measure the die temperature of other ICs, such as microprocessors, that contain an on-chip, diode-connected transistor.
The 2-wire serial interface accepts standard system management bus (SMBus™) write byte, read byte, send byte, and receive byte commands to program the alarm thresholds and to read temperature data. The data format is 7 bits plus sign, in two's-complement format.


Is to connect the small QSOP package MAX1668 comes in. Each pin is 0.25mm wide, and there is one pin each 0.6 mm. That is : "on less than 5mm there is 8 pins to solder". The easy way is to buy SMT adapterboards,

This is the Bascom code example I used. The code uses 74% of the available 2Kb of the AT90S2313. A demo version (4Kb limit) of Bascom can be downloaded here

    The code does the following:
  • Read Manufacture ID
  • Read Device ID
  • Read Status byte 1
  • Read Status byte 2
  • Read MAX1668 Local Temperature
  • Set remote DX1 Thigh limit
  • Set remote DX1 Tlow limit
  • Read Remote DX1 Thigh limit
  • Read Remote DX1 Tlow limit
  • Read Remote DX1 temperature 10 times with a 1sec. interval

  • There is much more possible with the MAX1668, the MAX1668 can generate an interrupt if a temperature is outside Thigh or Tlow limits for example. Consult the datasheet for an overview of all available commands.

    Bascom example program :

    ' Application Note: Using the MAX1668
    ' Program-ID.: MAX1668.bas.
    ' Date...... : 22 / 05 / 2005
    ' Description: Example program for MAX1668 Multichannel Remote/Local
    ' Temperature Sensors
    ' write and read routines.
    ' Author : Roland van leusden (
    ' Setup for the AT90S2313 using portd.6 for SDA and Portd.5 for SCL.
    ' (Futurlec ET-JRAVR board)
    ' See page 1 from MAX1668 datasheet for shematic. (
    ' This program provides an example for writing to and reading from
    ' a MAX1668 device wired with AO,A1 open.
    $regfile = "2313def.dat" ' Change for your AVR.
    $crystal = 4000000 ' 4 MHz Crystal.
    $baud = 19200  ' Output at 19200 baud.

    '** Set up Data Direction Registers and ports - Do this before defining I2C pins!
    ' Port B
    Portb = &B0000_0000 ' Set All Port Pins Low
    Ddrb = &B1111_1111 ' Set Unused Pins As Outputs.
    ' Port D
    Portd = &B0000_0000 ' All low - with push-pull output
    Ddrd = &B1111_1111 ' with internal pullups.

    '** Define and initialize I2C pins **
    Config Sda = Portd.6 ' I2C Data.
    Config Scl = Portd.5  ' I2C Clock.


    '** Declare subroutines **
    ' This subroutine writes data to the I2C MAX1668.
    Declare Sub I2c_max1668_write(byval Cmd As Byte , Byval Msb As Byte)
    ' This subroutine reads data from the I2C MAX1668.
    Declare Sub I2c_max1668_read(byval Cmd As Byte , Msb As Byte)
    '** Define working variables and constants **

    Dim Max1668_adress_w As Byte
    = &H54 'A1 & A0 open, see datasheet

    Dim Max1668_adress_r As Byte
    = &H55 'A1 & A0 open, see datasheet

    Dim Counter_1 As Byte
    Dim Cmd As Byte
    Dim Msb As Byte

    '** Actual work starts here. **


    = &H00
    Call I2c_max1668_read(&Hfe , Msb) ' Read MSB
    Print "Manufacture ID : " ; Hex(msb) ' MSB to serial port

    = &H00
    Call I2c_max1668_read(&Hff , Msb)  ' Read MSB
    Print "Device ID : " ; Hex(msb) ' MSB to serial port

    = &H00
    Call I2c_max1668_read(&H05 , Msb) ' Read MSB
    Print "Status byte 1 : " ; Bin(msb) ' MSB to serial port

    = &H00
    Call I2c_max1668_read(&H06 , Msb) ' Read MSB
    Print "Status byte 2 : " ; Bin(msb) ' MSB to serial port

    = &H00
    Call I2c_max1668_read(&H00 , Msb) ' Read MSB
    Print "MAX1668 Local Temperature: " ; Msb ' MSB to serial port

    = &H09
    Call I2c_max1668_write(&H15 , Msb) ' Write remote DX1 THIGH limit

    = &H00
    Call I2c_max1668_write(&H16 , Msb) ' Write remote DX1 Tlow limit

    = &H00
    Call I2c_max1668_read(&H0a , Msb) ' Read MSB
    Print "Remote DX1 Thigh limit: " ; Msb ' MSB to serial port

    = &H00
    Call I2c_max1668_read(&H0b , Msb) ' Read MSB
    Print "Remote DX1 Tlow limit: " ; Msb ' MSB to serial port

    = 0


    = &H00
    Call I2c_max1668_read(&H01 , Msb) ' Read MSB
    Print "Remote DX1 temperature: " ; Msb ' MSB to serial port
    Wait 1
    = Counter_1 + 1

    Loop Until Counter_1 = 10

    End 'end program

    '** Define Subroutines **
    Sub I2c_max1668_write(byval Cmd As Byte , Msb As Byte)
    ' Writes data to the I2C MAX1668.

    I2cstart 'Generate A Start Condition
    I2cwbyte Max1668_adress_w 'Transmit The "ADDRESS and WRITE" Byte
    I2cwbyte Cmd  'Transmit The Command Byte
    I2cwbyte Msb 'Transmit Data Byte
    I2cstop 'Generate a STOP condition
    'Waitus 50  'Some delay may be necessary for back to back transmitions

    End Sub

    Sub I2c_max1668_read(byval Cmd As Byte , Msb As Byte)
    ' Read data from the I2C MAX1668

    I2cstart 'Generate START condition
    I2cwbyte Max1668_adress_w 'Transmit The "ADDRESS and WRITE" Byte
    I2cwbyte Cmd 'Transmit The Command Byte
    I2cstart  'Generate a REPEATED-START condition
    I2cwbyte Max1668_adress_r 'Transmit ADDRESS with READ command
    I2crbyte Msb , Nack 'Receive DATA byte (MSB) and don't acknowledge
    I2cstop 'Generate a STOP condition

    End Sub

    Original pages are here