1.3. GPIO Pin Expansion Using I2C Bus Interface Using MAX II Devices
The detailed description of the implementation is based on the MAX II devices. This application can also be implemented in MAX V and MAX 10 devices.
Figure 3. GPIO Pin Expansion Demonstration Circuit
Implementation involves using this design example source code and allocating I2C bus lines and GPIO pin expansion inputs and outputs to MAX II GPIOs. GPIO pin expansion is demonstrated on the MDN-B2 demo board with the help of an I2C simulator that is created using a PC parallel port and interfacing hardware to create an I2C compliant two-wire bus.
Details about setting up an I2C environment is described in the Dallas Semiconductor's Maxim application note AN3230. This utility program uses the parallel port and its interfacing hardware to interact with the MAX II device and provides the SDA and SCL connections, as required on an I2C two-wire system. When implemented, this design allows inputs from the MDN-B2 demo board (set via DIP switches) to reach the I2C master. Similarly, data sent by the I2C master is available on the GPIO output ports (connected to LEDs on the demo board) of the MAX II device. The I2C master in this demonstration is the user interface on the PC running the parallel port I2C software.
The following details the implementation of this design example on the MDN-B2 demo board.
| Signal | Pin | Signal | Pin |
|---|---|---|---|
| SCLK | pin 39 | SDA | pin 40 |
| GPIO_output[0] | pin 69 | GPIO_output[1] | pin 70 |
| GPIO_output[2] | pin 71 | GPIO_output[3] | pin 72 |
| GPIO_output[4] | pin 73 | GPIO_output[5] | pin 74 |
| GPIO_output[6] | pin 75 | GPIO_output[7] | pin 76 |
| GPIO_input[0] | pin 55 | GPIO_input[1] | pin 56 |
| GPIO_input[2] | pin 57 | GPIO_input[3] | pin 58 |
| GPIO_input[4] | pin 61 | GPIO_input[5] | pin 66 |
| GPIO_input[6] | pin 67 | GPIO_input[7] | pin 68 |
Note: Assign unused pins As input-tristated in the Quartus® II software. You must also enable the Auto Open-Drain setting on the SCLK and SDA pins. To do this, on the Assignments menu, click Settings and then select Analysis and Synthesis Settings to enable the Auto Open-Drain setting. These settings are followed by a compilation cycle.