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diff --git a/source/i2c.rst b/source/i2c.rst index 34bd57c..564ca0e 100644 --- a/source/i2c.rst +++ b/source/i2c.rst @@ -4,4 +4,89 @@ |i2c| ===== -Stub. +.. note:: + + The i2c interface is currently only available from the 'i2c' branch + of the github `libmaple <http://github.com/leaflabs/libmaple>`_ + repository. + +|i2c| is a crude and easy-to-hack serial protocol that requires only +two wires/channels for communication between many devices. Every +message passed on the bus is between a *master* (who initiates the +message) and a *slave* device. Slaves are addressed using 7-bit +addresses (up to 127 unique devices); 10-bit addressing is possible, +but currently unimplemented. Every message consists of an arbitrary +combination of 8-bit reads and writes as requested by the master. +Higher level functionality, such as reading a particular register +value, is achieved by writing to set the memory location then reading +to pull out the data. + +Note that the master/slave designation is on a message-by-message +basis. The Maple can act as both a master (messages initiated by user +code) and slave device (responding to requests via configurable +interrupt handlers) at the same time. + +.. contents:: Contents + :local: + +Hardware/Circuit Design +----------------------- + +The Maple has two |i2c| ports. Port 1 (i2c1) has SDA on header D9 and +SCL on D5; Port 2 (i2c2) has SDA on D30 and SCL on D29. + +The Maple reliably communicates with up to a 400kHz clock speed; this +doesn't translate into a 400kbps data rate except in extreme cases +because of addressing and protocol overhead. We have tested clock +speeds up to a megahertz and have had mixed results; in theory it +could be possible to achieve even higher rates, but signal quality +degrades rapidly and the bus becomes unreliable. + +Proper wiring and pull-up resistor selection are essential when +incorporating |i2c| into a circuit, especially with data rates above +100kHz. In the lab, we usually use approximately 5kΩ resistors with +|vcc| (3.3V) as the high voltage, and try to connect the pullup +voltage as close to the SDA and SCL pins as possible. We recommend +looking at the ST reference website for |i2c| (see the +:ref:`recommended reading <i2c-recommended-reading>` below), starting +with a slow clock rate (10kHz), and, if possible, using an +oscilloscope to debug any issues. + +Function Reference +------------------ + +The function API for |i2c| is not finished! See the `source code +<http://github.com/leaflabs/libmaple/blob/i2c/libmaple/i2c.h>`_ for +now. + +.. TODO link to libmaple I2C docs once (1) finished, (2) in master + +SMBus +----- + +The STM32 microcontroller has hardware support for SMBus; we simply +have not written software for it. The SMBAL line for i2c1 is on header +D4 and for i2c2 is on D31. + +.. TODO link to libmaple SMBus docs once (1) finished, (2) in master + +.. _i2c-recommended-reading: + +Recommended Reading +------------------- + +* `i2c-bus.org <http://www.i2c-bus.org/>`_ +* `Wikipedia Article on i2c <http://en.wikipedia.org/wiki/I%C2%B2C>`_ +* `Arduino i2c/TWI reference <http://www.arduino.cc/playground/Learning/I2C>`_ +* STMicro documentation for STM32F103RB microcontroller: + + * `All <http://www.st.com/mcu/devicedocs-STM32F103RB-110.html>`_ + * `Datasheet + <http://www.st.com/stonline/products/literature/ds/13587.pdf>`_ + (pdf) + * `Reference Manual + <http://www.st.com/stonline/products/literature/rm/13902.pdf>`_ + (pdf) + * `Application Note on Advanced I2C Usage + <http://www.st.com/stonline/products/literature/an/15021.pdf>`_ + (pdf) |