SMBus note

Author: electronicayciencia

docs/source/gui.rst

@@ -3,8 +3,7 @@ Graphical interface
 
 *EasyMCP2221 Workbench* is a graphical application to configure and play with MCP2221 and MCP2221A chips based on EasyMCP2221 library.
 
-https://github.com/electronicayciencia/EasyMCP2221-GUI
-
+`EasyMCP2221 Workbench GitHub <https://github.com/electronicayciencia/EasyMCP2221-GUI>`_ (source code, screenshots and pre-compiled binaries for Windows available).
 
 .. figure:: https://github.com/electronicayciencia/EasyMCP2221-GUI/raw/main/screenshots/main_window.png
 

docs/source/history.rst

@@ -12,7 +12,7 @@ V1.7.1
 
 I2C:
     * Set I2C default speed to 100kHz. In some chips, the default speed is 500kHz and can cause trouble with some slave devices or noisy buses. You can adjust it with :func:`I2C_speed` function.
-    * Add clock frequency parameter in SMBus class.
+    * Added clock frequency parameter in SMBus class.
 
 Misc:
     * Added function :func:`revision` to get the mayor and minor hardware and firmware revision.

docs/source/smbus.rst

@@ -12,7 +12,7 @@ Usage:
 
     from EasyMCP2221 import SMBus
 
-    bus = SMBus(1)
+    bus = SMBus()
 
 
 or
@@ -21,11 +21,19 @@ or
 
     from EasyMCP2221 import smbus
 
-    bus = smbus.SMBus(1)
+    bus = smbus.SMBus()
+
+
+.. note::
+
+  To use other mcp functions in addition to SMBus, do not create a new MCP Device.
+  It will interfere with existing bus resulting in unpredictable behavior.
+  Always re-use ``bus.mcp`` object (see `example 2`).
 
 
-Example
--------
+
+Example 1: Basic weather station
+--------------------------------
 
 In this example, we are using a library from `Pimoroni/BME280 <https://github.com/pimoroni/bme280-python>`_ to read Temperature, Barometric Pressure and Relative Humidity from a BME280 sensor.
 
@@ -69,6 +77,70 @@ Output:
     ...
 
 
+
+Example 2: Real Time Clock with LCD
+-----------------------------------
+
+This is a digital clock with two I2C chips:
+
+* DS1307 as RTC
+* LCD display based on with PCF8574 I2C adapter.
+
+It also shows how to re-use ``mcp`` object to further configure MCP2221.
+
+Main loop:
+
+- DS1307 is configured as 1Hz square oscillator.
+- MCP2221's GP2 is configured as Interrupt on Change.
+- The rising edge of DS1307's output triggers the update cycle.
+
+Full code on `EasyMCP2221 examples/clock <https://github.com/electronicayciencia/EasyMCP2221/tree/master/examples/clock>`_
+
+
+.. code-block:: python
+
+    from EasyMCP2221 import SMBus
+    from lcd_driver import LCD
+    from DS1307 import DS1307
+
+    # Create SMBus and instances
+    bus = SMBus()
+    lcd = LCD(bus, addr=0x3F)
+    ds = DS1307(bus, addr=0x68)
+
+    bus.mcp.I2C_speed(100_000) # DS1307 only supports 100kHz
+
+    bus.mcp.set_pin_function(
+        gp0 = "GPIO_IN",  # unused
+        gp1 = "IOC",      # trigger update LCD each second
+        gp2 = "DAC",      # simulate backup battery
+        gp3 = "LED_I2C")  # i2c traffic indicator
+
+    bus.mcp.DAC_write(21) # about 3.28V with 5V Vcc
+    bus.mcp.IOC_config(edge = "rising")
+
+    # Initialization after a complete power loss
+    if ds.halted():
+        ds.write_now()
+        ds._write(0x07, 0b0001_0000) # sqwe 1Hz
+        print("RTC initialized with current timestamp")
+    else:
+        print("RTC was already initialized")
+
+    lcd.clear()
+
+    # Update only when GP1 changes using Interrupt On Change
+    while True:
+        if bus.mcp.IOC_read():
+            bus.mcp.IOC_clear()
+            (year, month, day, dow, hours, minutes, seconds) = ds.read_all()
+
+            lcd.display_string("%02d/%02d/20%02d" % (day, month, year), 1)
+            lcd.display_string("%02d:%02d:%02d" % (hours, minutes, seconds), 2)
+
+
+
+
 Full reference
 --------------
 

examples/clock/clock.py

@@ -17,10 +17,10 @@
 bus.mcp.I2C_speed(100_000) # DS1307 only supports 100kHz
 
 bus.mcp.set_pin_function(
-    gp0 = "GPIO_OUT", # updating monitor
-    gp1 = "IOC",      # update LCD each second
-    gp2 = "GPIO_IN",  # unused
-    gp3 = "DAC")      # simulate backup battery
+    gp0 = "GPIO_IN",  # unused
+    gp1 = "IOC",      # trigger update LCD each second
+    gp2 = "DAC",      # simulate backup battery
+    gp3 = "LED_I2C")  # i2c traffic indicator
 
 bus.mcp.DAC_write(21) # about 3.28V with 5V Vcc
 bus.mcp.IOC_config(edge = "rising")
@@ -39,10 +39,7 @@
 while True:
     if bus.mcp.IOC_read():
         bus.mcp.IOC_clear()
-        bus.mcp.GPIO_write(gp0 = True) # updating start
         (year, month, day, dow, hours, minutes, seconds) = ds.read_all()
 
-        #print(year, month, day, dow, hours, minutes, seconds)
         lcd.display_string("%02d/%02d/20%02d" % (day, month, year), 1)
         lcd.display_string("%02d:%02d:%02d" % (hours, minutes, seconds), 2)
-        bus.mcp.GPIO_write(gp0 = False) # updating end