Summary of Extend I/O Ports using PIC Microcontroller
This article details the mikroC PRO for PIC library enabling SPI communication with the Microchip MCP23S17 Port Expander. It outlines necessary external variable definitions for reset and chip select lines, specifies that the SPI module must be pre-initialized, and lists various routines for initialization, byte I/O, port reading/writing, and direction/pull-up configuration.
Parts used in the MikroC PRO for PIC Port Expander Project:
- Microchip MCP23S17 Port Expander
- PIC compliant MCU
- SPI module
- Reset line (SPExpanderRST)
- Chip Select line (SPExpanderCS)
- Port A pins
- Port B pins
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 :
Parameters :
|
| Requires | Global variables :
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(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 :
|
| Requires |
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 :
|
| 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 :
|
| 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 :
|
| 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); |
Expander_Read_PortB
| Prototype | char Expander_Read_PortB(char ModuleAddress); |
|---|---|
| Returns | Byte read. |
| Description | The function reads byte from Port Expander’s PortB. Parameters :
|
| Requires | Port Expander must be initialized.
Port Expander’s PortB should be configured as input. |
| Example |
// Read a byte from Port Expander's PORTB char read_data; ... Expander_Set_DirectionPortB(0,0xFF); // set expander's portb to be input ... read_data = Expander_Read_PortB(0); |
For more detail: Extend I/O Ports using PIC
- How do you initialize the Port Expander?
The user must first initialize the appropriate SPI module before using the library functions like Expander_Init. - What variables must be defined in all projects?
Variables for the Reset line, Chip Select line, and their respective directions must be defined externally. - Does the library use interrupts?
No, the library does not use Port Expander interrupts. - Can you read data from specific ports?
Yes, functions like Expander_Read_PortA and Expander_Read_PortB allow reading bytes from specific ports. - How do you configure a port as input?
You use routines like Expander_Set_DirectionPortA or Expander_Set_DirectionPortB to set the direction. - What parameters are required for Expander_Init?
The function requires the ModuleAddress which represents the Port Expander hardware address. - Is hardware addressing enabled by default?
Yes, the standard Expander_Init enables hardware addressing. - Can you write a byte to a register?
Yes, the Expander_Write_Byte routine writes a byte to the Port Expander's internal register address. - What is the best way to handle digital I/O configuration?
The example code suggests setting ANSEL and ANSELH to 0 to configure analog pins as digital I/O.
