This application note describes how to use a PIC16F877A as an I 2 C™ master to communicate with the Microchip MCP23016 I 2 C I/O Expander slave device. An I/O Expander device is used to increase the I/O capability of a microcontroller (refer to Figure 1). A microcontroller’s I 2 C port can be used as a communi- cation channel with MCP23016(s) to expand the micro- controller’s I/O count. By using two I 2 C pins (and one general-purpose I/O pin, if using the interrupt capability of the MCP23016), 16 to 128 general-purpose I/Os can be gained. The MCP23016 has three address pins which can be used to provide unique addresses for up to eight devices. Each device attached to the I 2 C bus must be assigned a unique address unless all devices (with the same address) are receiving the same data and do not trans- mit any data. When the master initiates a data transfer, the address of the slave device is transmitted. Within the address, the LSb (R/W bit) specifies whether the master reads from, or writes to, the slave. For write operations, a series of bytes would be transmitted from the master. For read operations, the master waits for the bus to be free (i.e., SCL line not pulled low) and then clocks the data to be received from the slave.M AN245 Interfacing The MCP23016 I/O Expander With The PIC16F877A What can you do with an I/O Expander? Author: Abdelwahab Fassi-Fihri Microchip Technology Inc. An I/O Expander can also be used to monitor switches and/or sensors, drive LEDs and/or relays, as well as other general-purpose I/O functions. An I/O Expander INTRODUCTION can have several uses in a variety of applications. Typ- This……