Diff: main.cpp

Revision:

0:12f4911d7ba0

Child:

1:70e1ebe47253

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Thu Jan 27 03:16:18 2011 +0000
@@ -0,0 +1,55 @@
+/* A simple IO demo using the MCP23S17 library
+* Copyright (c) 2010 Romilly Cocking
+* Released under the MIT License: http://mbed.org/license/mit
+*
+* See http://mbed.org/users/romilly/notebook/mcp23s17-addressable-16-bit-io-expander-with-spi/
+*
+
+* MCP23S17 datasheet http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf
+* version 0.4
+*/
+#include "mbed.h"
+#include "MCP23S17.h"
+
+SPI spi(p5, p6, p7);
+// Create SPI bus
+// mbed p5,p6,p7 are tied to MCP23S17 SI, SO, SCK pins
+// A0, A1, A2 of the MCP23S17  are tied to ground on the breadboard, so the 8-bit address for writes is 0x40
+// This is referred to as the opcode in the device datasheet
+char writeOpcode = 0x40;
+
+// Next create a MCP23S17
+// mbed p20 is connected to ~chipSelect on the MCP23S17
+MCP23S17 chip = MCP23S17(spi, p20, writeOpcode);
+
+DigitalOut led1(LED1); // mbed LED1 is used for test status display
+
+int main() {
+//  Nothing has to be connected to the MCP23S17 reset pin since it has a power on reset circuit.
+//  It can be used for a software forced reset by pulling it low with an mbed GPIO pin.
+//  But just leave it unconnected for this simple demo code. It is possible to lock up the chip
+//  if you happen to reset the mbed in the middle of an SPI transfer (not too likely). 
+//  If it happens just remove and attach the USB cable to reset by cycling the power.
+//  After a power on reset, both IO ports default to input mode
+//
+//  Set all 8 Port A bits to output direction
+    chip.direction(PORT_A, 0x00);
+//  Set all 8 Port B bits to input direction
+    chip.direction(PORT_B, 0xFF);
+    led1=0;
+//  Start Loopback test sending out and reading back values
+//  loopback test uses A0 and B0 pins - so use a wire to jumper those two pins on MCP23S17 together
+    while (1) {
+        // write 0xAA to MCP23S17 Port A
+        chip.write(PORT_A, 0xAA);
+        wait(.5);
+        // read back value from MCP23S17 Port B and display B0 on mbed led1
+        led1 = chip.read(PORT_B)& 0x01;
+        // write 0x55 to MCP23S17 Port A
+        chip.write(PORT_A, 0x55);
+        wait(.5);
+        // read back value from MCP23S17 Port B and display B0 on mbed led1
+        led1 = chip.read(PORT_B)& 0x01;
+        // led1 should blink slowly if it is all working
+    }
+}