General-Purpose I/O Lines

The EM1206 has 17 general-purpose I/O (GPIO) lines (GPIO0 ~ GPIO16). All lines are 3.3V, CMOS, and 5V-tolerant. The maximum load current for each line is 10mA. Out of 17 available lines, 16 are combined into two 8-bit ports.

The simplified structure of one I/O line of the EM1206 is shown in the circuit diagram below. Each line has an independent output buffer control. When the EM1206 powers up, all I/O lines have their output buffers tri-stated (in other words, all I/O lines are configured as inputs). You need to explicitly enable the output buffer of a certain I/O line if you want this line to become an output.

Each I/O line has a weak pull-up resistor that prevents the line from floating when the output buffer is tri-stated. I/O line control is described in the io. object documentation.

A circuit diagram of an EM1206 GPIO line.

Many I/O lines of the EM1206 have alternative functions and serve as inputs or outputs of special function modules: On the EM1206, the special function modules are four serial ports and the square wave generator. When any special function module is enabled, its I/O lines seize to work as inputs/outputs and are controlled by this special function module directly. Depending on the nature of an alternative function a given I/O line is to perform, your application may still have to manually configure this line for input or output. The table below details which special function module lines require manual configuration:

RX lines of serial ports	Automatically configured as inputs when a corresponding serial port is enabled, revert to previous state when this port is disabled.
TX lines of serial ports	Automatically configured as outputs when a corresponding serial port is enabled, revert to previous state when this port is disabled.
CTS lines of serial ports	Must be configured as inputs by your application. Note that CTS lines can be "remapped".
RTS lines of serial ports	Must be configured as outputs by your application. Note that RTS lines can be "remapped".
CO (square wave output)	Automatically configured as output when the square wave is being generated, reverts to previous state when the square wave output stops.