Diff: PCA9544a.h

Revision:

2:31aceaca418e

Parent:

1:4d19097c0571

diff -r 4d19097c0571 -r 31aceaca418e PCA9544a.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PCA9544a.h	Thu Sep 14 00:20:57 2017 +0000
@@ -0,0 +1,103 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017 AT&T, IIoT Foundry, Plano, TX, USA
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** \addtogroup drivers */
+
+/** Support for the NXP PCA9544A 4-channel I2C switch.
+ *
+ * Example:
+ * @code
+ *
+ * #include "mbed.h"
+ * #include "PCA9544A.h"
+ *
+ * // PCA9544A strapped for address option 0 (7-bit I2C address 0x70)
+ *
+ * I2C            i2c(I2C_SDA, I2C_SCL);
+ * PCA9544A<I2C>  pca9544a(&i2c, 0);
+ *
+ * int main() {
+ *     bool                ok;
+ *
+ *     // Enable channel 1
+ *     bool ok = _pca9544a->select_channel(1);
+ *     if (ok) {
+ *         printf("I2C device on channel 1 is now accessible\r\n);
+ *     } else {
+ *         printf("pca9544a error!\r\n");
+ *     }
+ *
+ *     // Disconnect all downstream devices from the I2C bus
+ *     _pca9544a->reset();
+ * }
+ * @endcode
+ * @ingroup drivers
+ */
+
+#pragma once
+
+#define PCA9544A_BASE_ADDR_7BIT     0x70
+#define MAX_CHANNELS                4
+
+template <class T>
+class PCA9544A
+{
+public:
+    /**
+    * Constructor
+    *
+    * @param i2c I2C class servicing the multiplexer
+    * @param addr_3bit address of the multiplexer (A0-A2 pin strapping)
+    *          Valid values are 0-7
+    */
+    PCA9544A(T * i2c, uint8_t addr_3bit) : _i2c(i2c) {
+        _addr_8bit = ((addr_3bit & 0x7) + PCA9544A_BASE_ADDR_7BIT) << 1;
+    }
+
+    /**
+    * Reset the multiplexer.  All devices connected to the downstream side of
+    * the multiplexer are removed from the I2C bus.  Reset is accomplished by
+    * deselecting all channels through soft configuration.
+    *
+    * @returns true if successful
+    */
+    bool reset(void) {
+        const char channel = 0;
+        return _i2c->write(_addr_8bit, &channel, 1) == 0;
+    }
+
+    /**
+    * Enable access to one of the eight devices on the downstream side of
+    * the multiplexer.
+    *
+    * @param channel channel to activate.  Valid values are 0-7.
+    *
+    * @returns true if successful
+    */
+    bool select_channel(const uint8_t channel) {
+        if (channel < MAX_CHANNELS) {
+            char channel_mask = 0x4 | channel;
+            return _i2c->write(_addr_8bit, (const char *)&channel_mask, 1) == 0;
+        } else {
+            return false;
+        }
+    }
+
+protected:
+    int     _addr_8bit;
+    T      *_i2c;
+};
+