5.2 KiB
I2C Overview
Helios64 support I2C bus for the low-speed communication between devices like microcontrollers, EEPROMs, A/D and D/A converters, I/O interface and other similar peripherals in embedded systems. In order to communicate with each I2C slave device you will need an address and communication scenario.
Please take caution of the reserved address when you use the I2C interface, below is the reseved address list:
| Slave Address | R/W Bit | Description |
|---|---|---|
| 000 0000 | 0 | General call address |
| 000 0000 | 1 | START byte(1) |
| 000 0001 | X | CBUS address(2) |
| 000 0010 | X | Reserved for different bus format (3) |
| 000 0011 | X | Reserved for future purposes |
| 000 01XX | X | Hs-mode master code |
| 111 10XX | X | 10-bit slave addressing |
| 111 11XX | X | Reserved for future purposes |
I2C bus on Helios64 / RK3399
The I2C controller on RK3399 support following features:
- 9 on-chip I2C controllers
- Multi-master I2C operation
- Support 7bits and 10bits address mode
- Serial 8bits oriented and bidirectional data transfers can be made
- Software programmable clock frequency
- Data on the I2C-bus can be transferred at rates of up to 100 kbit/s in the Standardmode, up to 400 kbit/s in the Fast-mode or up to 1 Mbit/s in Fast-mode Plus.
Internal Bus (system reserved, NOT for user application)
In the implementation, we divide the I2C controller into 2 category. The first implementation is for system (internal bus) and the other one is for user application (external). Below figure describe the I2C Map inside the board:
Bus 0:
| Slave | Address | Description |
|---|---|---|
| RK808-D | 0x1b | |
| SYR837 | 0x40 | |
| SYR838 | 0x41 |
Bus 2:
| Slave | Address | Description |
|---|---|---|
| NCT75 | 0x4c | |
| PCA9655 | 0x21 |
Bus 4:
| Slave | Address | Description |
|---|---|---|
| FUSB302 | 0x22 |
Above bus number and also including bus number 1,3,5 are reserved for system use, therefore not accessible to the user.
!!! Warning This bus number and address should not be accessed directly by user. Incorrect configuration can damaged the board!
External Bus
Helios64 exposed Bus number 7 and 8 of the I2C in P2 and P1 pinout, respectively. This I2C bus can be connected to the external devices.
As described on below figure of I2C (pin header number 3 and 4), user can access the device at bus number 7. For the UEXT (pin header number 5 and 6), user can access the device at bus number 8.
All the I2C bus in the board are using voltage level of 3.3V, please notice Helios64 is integrated with level translator and pull up resistor.
I2C at P1 Header
Helios64 board exposes the SoC I2C Bus 1, on header P1. Below is the header pin-out.
This I2C device working with 3 pin bus (SDA, SCK, and GND), and also in band addressing. We can use a 7 bit addressing to distinguish every device, but some address is reserved for the internal communication of the Helios64 board.
I2C at UEXT
The I2C header bus also can be found at UEXT connector (can be found at P2 header at the the board overview page) on the header number 5 and 6. Below is the detail description of the UEXT connector:
| Pin No | Description |
|---|---|
| 1 | 3.3V |
| 2 | GND |
| 3 | TXD (UART) |
| 4 | RXD (UART) |
| 5 | SCL (I2C) |
| 6 | SDA (I2C) |
| 7 | MISO (SPI) |
| 8 | MOSI (SPI) |
| 9 | SCK (SPI) |
| 10 | SSEL (SPI) |
Usage under Linux
External bus block device under linux
Below table describe the external bus of I2C under Linux,
| Bus number | Device Block | Description |
|---|---|---|
| 7 | /dev/i2c-7 | |
| 8 | /dev/i2c-8 |
Checking the I2C Communication under linux
In order to communicate with the I2C devices, first we need to identify the I2C bus. By performing scan you can see wether system detect the devices.
We can follow this step to perform the scanning process:
- Install the Linux i2c tools.
$ sudo apt-get install i2c-tools
- Use i2cdetect tool to scan I2C Bus 1.
root@helios64:~# i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
Here we can see there is a device detected at the address 0x3c. We can conclude is our OLED screen, unless you have connected more than just one I2C device on the J9 header.
Application example
We have demonstrated the use of I2C bus of our board in the OLED application, as shown in the I2C(OLED) page you can communicate to the external device by using the external I2C bus.