MCP23S17_Basic_IO_Demo - A simple IO demo using the MCP23S17 library

Users » 4180_1 » Code » MCP23S17_Basic_IO_Demo

jim hamblen / Mbed 2 deprecated MCP23S17_Basic_IO_Demo

A simple IO demo using the MCP23S17 library

Demo for Microchip MCP23S17 16-bit SPI I/O expander chip on mbed LPC1768 using hardware SPI functions. See comments in main.cpp for pin usage. This chip is still available in a DIP package, so it is easy to try on a breadboard. A complete datasheet for the Microchip MCP23SA17 SPI I/O port expander chip can be found at http://ww1.microchip.com/downloads/en/DeviceDoc/20001952c.pdf

Import program MCP23S17_Basic_IO_Demo

A simple IO demo using the MCP23S17 library

main.cpp@1:70e1ebe47253, 2011-01-28 (annotated)

Committer:: 4180_1
Date:: Fri Jan 28 01:44:27 2011 +0000
Revision:: 1:70e1ebe47253
Parent:: 0:12f4911d7ba0
Child:: 2:934a0500abde

Who changed what in which revision?

User	Revision	Line number	New contents of line
4180_1	0:12f4911d7ba0	1	/* A simple IO demo using the MCP23S17 library
4180_1	0:12f4911d7ba0	2	* Copyright (c) 2010 Romilly Cocking
4180_1	0:12f4911d7ba0	3	* Released under the MIT License: http://mbed.org/license/mit
4180_1	0:12f4911d7ba0	4	*
4180_1	0:12f4911d7ba0	5	* See http://mbed.org/users/romilly/notebook/mcp23s17-addressable-16-bit-io-expander-with-spi/
4180_1	0:12f4911d7ba0	6	*
4180_1	0:12f4911d7ba0	7
4180_1	0:12f4911d7ba0	8	* MCP23S17 datasheet http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf
4180_1	0:12f4911d7ba0	9	* version 0.4
4180_1	0:12f4911d7ba0	10	*/
4180_1	0:12f4911d7ba0	11	#include "mbed.h"
4180_1	0:12f4911d7ba0	12	#include "MCP23S17.h"
4180_1	0:12f4911d7ba0	13
4180_1	0:12f4911d7ba0	14	SPI spi(p5, p6, p7);
4180_1	0:12f4911d7ba0	15	// Create SPI bus
4180_1	0:12f4911d7ba0	16	// mbed p5,p6,p7 are tied to MCP23S17 SI, SO, SCK pins
4180_1	0:12f4911d7ba0	17	// A0, A1, A2 of the MCP23S17 are tied to ground on the breadboard, so the 8-bit address for writes is 0x40
4180_1	0:12f4911d7ba0	18	// This is referred to as the opcode in the device datasheet
4180_1	0:12f4911d7ba0	19	char writeOpcode = 0x40;
4180_1	0:12f4911d7ba0	20
4180_1	0:12f4911d7ba0	21	// Next create a MCP23S17
4180_1	0:12f4911d7ba0	22	// mbed p20 is connected to ~chipSelect on the MCP23S17
4180_1	0:12f4911d7ba0	23	MCP23S17 chip = MCP23S17(spi, p20, writeOpcode);
4180_1	0:12f4911d7ba0	24
4180_1	1:70e1ebe47253	25	// Optional software reset - mbed p20 to MCP23S17 reset pin
4180_1	1:70e1ebe47253	26	// DigitalOut reset(p20);
4180_1	1:70e1ebe47253	27
4180_1	0:12f4911d7ba0	28	DigitalOut led1(LED1); // mbed LED1 is used for test status display
4180_1	0:12f4911d7ba0	29
4180_1	0:12f4911d7ba0	30	int main() {
4180_1	1:70e1ebe47253	31	// The MCP23S17 reset pin can just be pulled high, since it has a power on reset circuit.
4180_1	1:70e1ebe47253	32	// The reset pin can be used for a software forced reset by pulling it low with an mbed GPIO pin.
4180_1	1:70e1ebe47253	33	// But just leave it pulled high for this simple demo code.
4180_1	0:12f4911d7ba0	34	// After a power on reset, both IO ports default to input mode
4180_1	0:12f4911d7ba0	35	//
4180_1	1:70e1ebe47253	36	// Here is the optional code for a software reset
4180_1	1:70e1ebe47253	37	// reset = 0;
4180_1	1:70e1ebe47253	38	// wait_us(1);
4180_1	1:70e1ebe47253	39	// reset = 1;
4180_1	1:70e1ebe47253	40	//
4180_1	0:12f4911d7ba0	41	// Set all 8 Port A bits to output direction
4180_1	0:12f4911d7ba0	42	chip.direction(PORT_A, 0x00);
4180_1	0:12f4911d7ba0	43	// Set all 8 Port B bits to input direction
4180_1	0:12f4911d7ba0	44	chip.direction(PORT_B, 0xFF);
4180_1	0:12f4911d7ba0	45	led1=0;
4180_1	0:12f4911d7ba0	46	// Start Loopback test sending out and reading back values
4180_1	0:12f4911d7ba0	47	// loopback test uses A0 and B0 pins - so use a wire to jumper those two pins on MCP23S17 together
4180_1	0:12f4911d7ba0	48	while (1) {
4180_1	0:12f4911d7ba0	49	// write 0xAA to MCP23S17 Port A
4180_1	0:12f4911d7ba0	50	chip.write(PORT_A, 0xAA);
4180_1	0:12f4911d7ba0	51	wait(.5);
4180_1	0:12f4911d7ba0	52	// read back value from MCP23S17 Port B and display B0 on mbed led1
4180_1	0:12f4911d7ba0	53	led1 = chip.read(PORT_B)& 0x01;
4180_1	0:12f4911d7ba0	54	// write 0x55 to MCP23S17 Port A
4180_1	0:12f4911d7ba0	55	chip.write(PORT_A, 0x55);
4180_1	0:12f4911d7ba0	56	wait(.5);
4180_1	0:12f4911d7ba0	57	// read back value from MCP23S17 Port B and display B0 on mbed led1
4180_1	0:12f4911d7ba0	58	led1 = chip.read(PORT_B)& 0x01;
4180_1	0:12f4911d7ba0	59	// led1 should blink slowly if it is all working
4180_1	0:12f4911d7ba0	60	}
4180_1	0:12f4911d7ba0	61	}