Router I2C Interface

These are the I2C Bus Hardware and Software settings I am using with the on OpenWrt Midge router to talk to a PIC 16F876 I2C Slave.

I2C Hardware

Here is the level shifter I’m using for the Router (3v) I2C interface (5v on Pic and other chips I have)

                 5v
                |
                |
                R
               4k7
                R
                |
SCL ---+--R220--+-----> 5v SCL
       |
     =====  Use the Same
      ZD\   For the Data
     /3.3\  Line
       |
       |
0v-----+---------------

The above has so far worked happily with an old philips 2048bit (256 bytes!) eeprom.

Pin Header (for breadboard)

1: 0v

2: 3v

3: 5v

4: KEY NC

5: TX (I/O Bus -> project)

6: RX (project <- I/O Bus)

7: LED3 GPIO8 I2C SDA

8: LED5 GPIO11 I2C SCL

I2C Software Settings

In the sunspot.co.uk Midge rom, the default I2C port uses different gpio lines.  To use gpio 8 and 11, the file “/etc/init.d/S99start_i2c” file needs changing:-

The line containing “insmod i2c-adm5128″ needs to read “insmod i2c-adm5120 scl=11 sda=8″