/*
- I2C using Parallel Port and custom driver project
- Path: i2cPpLKM */
Used parallel port cable split open PP Pin2 is SCL PP Pin3 is SDA out PP Pin12 is SDA in SDA and SCL are buffered using open drain inverter (7406N)
I2C device, 24AA1025 from Microchip, digikey PN: 24AA1025-I/P-ND, IC EEPROM 1MBIT 400KHZ 8DIP Pin 1, A0, VSS Pin 2, A1, VSS Pin 3, A2, VCC Pin 4, VSS, VSS Pin 5, SDA, SDA Pin 6, SCL, SCL Pin 7, WP, VSS Pin 8, VCC, VCC
VCC is 5V.
Connections: Pin2 of PP to Pin1 of 7406N, 10k pull up resistor (to VCC) Pin2 of 7406N to device, 10k pull up resistor Pin3 of PP to Pin3 of 7406N, 10k pull up resistor Pin4 of 7406N to device, 10k pull up resistor Pin4 of 7406N to Pin5 of 7406N (handle device SDA signals) Pin12 of PP to Pin6 of 7406N, 10k pull up resistor
I was using the Arduino Uno to provide the 5V VCC but I recieved my USB breakout cable and used the +5V and Common from that
Debugging: After ironing out the algorithm on the Arduino Uno, I chose to use two 8-bit serial-in-parallel-out shift registers Outputs sink current lighting the LED's when 0 is entered for that register Shift registers used: STP08DP05 VCC 5V RExt 10k for Red LED and 2k for Yellow LED Without sending start/stop conditions, you can validate the data being sent to the device (notice the inversion on i2c_setSCL and i2c_setSDA) For driver debugging I used printk's all over and gradually removed them I also grabbed the Arduino Uno to verify the writes were taking place
There are far better drivers out there, with far greater complexity, using IOCTL for example. Here I used a simple character driver and modified it to perform inb/outb against the parallel port addresses (0x378/379)
This is something I have wanted to do for a very long time and though it took a lot longer than I had hoped, at least it is working to the point where I can release it for others to build upon/correct/learn from.
// Usage (as root, or prefix with "sudo" ): make insmod i2c.ko tail -n 2 /var/log/messages ** or /var/log/kern.log or /var/log/syslog depending on your distro - look for major number, system will assign it for you mknod /dev/i2c c 243 0 ** /dev/xxx the name you want the device to be, 243 is the major number, 0 is the minor number chmod 666 /dev/i2c ** ensure regular users can read/write to the "file", which the driver will handle as reading/writing
When writing, say with fwrite, the first byte is a control byte: 0x00 - nothing 0x01 - send i2c start 0x02 - send i2c stop 0x03 - send i2c start then at the end send i2c stop
After the control byte you typically send the device address then the data. For the 24AA1025, you send 0xA0 for a write, then two addresses, first is the high address byte, then the low address byte, then the data to be written, upt to 128 chars (the size of one page, any more data written will simply be overwritten by the device as it implements a circular buffer).
For a read, 0xA1 (bit 0 is 1 for read, 0 for write, bits7:4 are 1010 for a control byte for the device), and the data will be read. Send another ACK if you want more data. Address read will be the last address written to. Ideally, you would write your data, then send a write config and two address bytes, but no data, then send a new start and read config and the device will return your data, up to 128B.
After 128 bytes you have to change the address with the write-config and data address bytes, then the read config.
The device you're using should specify the protocol details for you. The LCD I tested this with was different from the SEEPROM I tested it with.