MCP23S17_Basic_IO_Demo - A simple IO demo using the MCP23S17 library

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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@0:12f4911d7ba0, 2011-01-27 (annotated)

Committer:: 4180_1
Date:: Thu Jan 27 03:16:18 2011 +0000
Revision:: 0:12f4911d7ba0
Child:: 1:70e1ebe47253

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	0:12f4911d7ba0	25	DigitalOut led1(LED1); // mbed LED1 is used for test status display
4180_1	0:12f4911d7ba0	26
4180_1	0:12f4911d7ba0	27	int main() {
4180_1	0:12f4911d7ba0	28	// Nothing has to be connected to the MCP23S17 reset pin since it has a power on reset circuit.
4180_1	0:12f4911d7ba0	29	// It can be used for a software forced reset by pulling it low with an mbed GPIO pin.
4180_1	0:12f4911d7ba0	30	// But just leave it unconnected for this simple demo code. It is possible to lock up the chip
4180_1	0:12f4911d7ba0	31	// if you happen to reset the mbed in the middle of an SPI transfer (not too likely).
4180_1	0:12f4911d7ba0	32	// If it happens just remove and attach the USB cable to reset by cycling the power.
4180_1	0:12f4911d7ba0	33	// After a power on reset, both IO ports default to input mode
4180_1	0:12f4911d7ba0	34	//
4180_1	0:12f4911d7ba0	35	// Set all 8 Port A bits to output direction
4180_1	0:12f4911d7ba0	36	chip.direction(PORT_A, 0x00);
4180_1	0:12f4911d7ba0	37	// Set all 8 Port B bits to input direction
4180_1	0:12f4911d7ba0	38	chip.direction(PORT_B, 0xFF);
4180_1	0:12f4911d7ba0	39	led1=0;
4180_1	0:12f4911d7ba0	40	// Start Loopback test sending out and reading back values
4180_1	0:12f4911d7ba0	41	// loopback test uses A0 and B0 pins - so use a wire to jumper those two pins on MCP23S17 together
4180_1	0:12f4911d7ba0	42	while (1) {
4180_1	0:12f4911d7ba0	43	// write 0xAA to MCP23S17 Port A
4180_1	0:12f4911d7ba0	44	chip.write(PORT_A, 0xAA);
4180_1	0:12f4911d7ba0	45	wait(.5);
4180_1	0:12f4911d7ba0	46	// read back value from MCP23S17 Port B and display B0 on mbed led1
4180_1	0:12f4911d7ba0	47	led1 = chip.read(PORT_B)& 0x01;
4180_1	0:12f4911d7ba0	48	// write 0x55 to MCP23S17 Port A
4180_1	0:12f4911d7ba0	49	chip.write(PORT_A, 0x55);
4180_1	0:12f4911d7ba0	50	wait(.5);
4180_1	0:12f4911d7ba0	51	// read back value from MCP23S17 Port B and display B0 on mbed led1
4180_1	0:12f4911d7ba0	52	led1 = chip.read(PORT_B)& 0x01;
4180_1	0:12f4911d7ba0	53	// led1 should blink slowly if it is all working
4180_1	0:12f4911d7ba0	54	}
4180_1	0:12f4911d7ba0	55	}