Extend I/O Ports using PIC Microcontroller

The mikroC PRO for PIC provides a library for communication with the Microchip’s Port Expander MCP23S17 via SPI interface. Connections of the PIC compliant MCU and MCP23S17 is given on the schematic at the bottom of this page.

  Important :

• The library uses the SPI module for communication. User must initialize the appropriate SPI module before using the Port Expander Library.
• Library does not use Port Expander interrupts.
  

  External dependencies of Port Expander Library

  The following variables must be defined in all projects using Port Expander Library:	Description :	Example :
  extern sfr sbit SPExpanderRST;	Reset line.	sbit SPExpanderRST at RC0_bit;
  extern sfr sbit SPExpanderCS;	Chip Select line.	sbit SPExpanderCS at RC1_bit;
  extern sfr sbit SPExpanderRST_Direction;	Direction of the Reset pin.	sbit SPExpanderRST_Direction at TRISC0_bit;
  extern sfr sbit SPExpanderCS_Direction;	Direction of the Chip Select pin.	sbit SPExpanderCS_Direction at TRISC1_bit;

  Library Routines

  • Expander_Init
  • Expander_Init_Advanced
  • Expander_Read_Byte
  • Expander_Write_Byte
  • Expander_Read_PortA
  • Expander_Read_PortB
  • Expander_Read_PortAB
  • Expander_Write_PortA
  • Expander_Write_PortB
  • Expander_Write_PortAB
  • Expander_Set_DirectionPortA
  • Expander_Set_DirectionPortB
  • Expander_Set_DirectionPortAB
  • Expander_Set_PullUpsPortA
  • Expander_Set_PullUpsPortB
  • Expander_Set_PullUpsPortAB

  Expander_Init

  Prototype	void Expander_Init(char ModuleAddress);
  Returns	Nothing.
  Description	Initializes Port Expander using SPI communication. Port Expander module settings :  hardware addressing enabled automatic address pointer incrementing disabled (byte mode) BANK_0 register adressing slew rate enabled Parameters : ModuleAddress: Port Expander hardware address, see schematic at the bottom of this page
  Requires	Global variables :  SPExpanderCS: Chip Select line SPExpanderRST: Reset line SPExpanderCS_Direction: Direction of the Chip Select pin SPExpanderRST_Direction: Direction of the Reset pin must be defined before using this function. SPI module needs to be initialized. See SPIx_Init and SPIx_Init_Advanced routines.
  Example	// Port Expander module connections sbit SPExpanderRST at RC0_bit; sbit SPExpanderCS at RC1_bit; sbit SPExpanderRST_Direction at TRISC0_bit; sbit SPExpanderCS_Direction at TRISC1_bit; // End Port Expander module connections ... ANSEL = 0; // Configure AN pins as digital I/O ANSELH = 0; // If Port Expander Library uses SPI module SPI1_Init(); // Initialize SPI module used with PortExpander Expander_Init(0); // Initialize Port Expander

  Expander_Init_Advanced

  Prototype	void Expander_Init_Advanced(char *rstPort, char rstPin, char haen);
  Returns	Nothing.
  Description	Initializes Port Expander using SPI communication. Parameters :  rstPort: Port Expander’s reset port rstPin: Port Expander’s reset pin haen: Enable hardware addressing. Valid values : 0 – hardware addressing disabled 1 – hardware addressing enabled
  Requires	SPExpanderCS: Chip Select line SPExpanderRST: Reset line SPExpanderCS_Direction: Direction of the Chip Select pin SPExpanderRST_Direction: Direction of the Reset pin must be defined before using this function.
  Example	// Port Expander module connections sbit SPExpanderRST at RC0_bit; sbit SPExpanderCS at RC1_bit; sbit SPExpanderRST_Direction at TRISC0_bit; sbit SPExpanderCS_Direction at TRISC1_bit; // End Port Expander module connections ... ANSEL = 0; // Configure AN pins as digital I/O ANSELH = 0; // If Port Expander Library uses SPI module SPI1_Init(); // Initialize SPI module used with PortExpander Expander_Init_Advanced(&PORTB, 0, 0); // Initialize Port Expander

   

  Expander_Read_Byte

  Prototype	char Expander_Read_Byte(char ModuleAddress, char RegAddress);
  Returns	Byte read.
  Description	The function reads byte from Port Expander. Parameters :  ModuleAddress: Port Expander hardware address, see schematic at the bottom of this page RegAddress: Port Expander’s internal register address
  Requires	Port Expander must be initialized.
  Example	// Read a byte from Port Expander's register char read_data; ... read_data = Expander_Read_Byte(0,1);

  Expander_Write_Byte

  Prototype	void Expander_Write_Byte(char ModuleAddress, char RegAddress, char Data);
  Returns	Nothing.
  Description	Routine writes a byte to Port Expander. Parameters :  ModuleAddress: Port Expander hardware address, see schematic at the bottom of this page RegAddress: Port Expander’s internal register address Data_: data to be written
  Requires	Port Expander must be initialized.
  Example	// Write a byte to the Port Expander's register Expander_Write_Byte(0,1,0xFF);

  Expander_Read_PortA

  Prototype	char Expander_Read_PortA(char ModuleAddress);
  Returns	Byte read.
  Description	The function reads byte from Port Expander’s PortA. Parameters :  ModuleAddress: Port Expander hardware address, see schematic at the bottom of this page
  Requires	Port Expander must be initialized.  Port Expander’s PortA should be configured as input.
  Example	// Read a byte from Port Expander's PORTA char read_data; ... Expander_Set_DirectionPortA(0,0xFF); // set expander's porta to be input ... read_data = Expander_Read_PortA(0);

  

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