Uno R3 with Wifi Shield, Uno I/O Pins sanity check

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Hi, I am new to Arduino. Apologies for my member ID, hadn't read the FAQ before creating it. I agree with the FAQ, though, it does sound funny.

I am adding a WiFi Shield to an Uno, and am trying to understand which Pins are used, and which are available. I would appreciate a double-check, and have a few questions below. This is what I understand so far:

The Uno uses 7 I/O Pins (including "L9") on the IOLow (0-7) and IOHigh headers (8-13).

There are 2 module selectors (one for each module):

  • Pin 10: WiFi Select
  • Pin 4: SD Select
    These are both low active. The associated libraries should manage these Pins when using both modules. However, if using only using one module, disable the other explicitly with digitalWrite(Pin, High).

There are 3 SPI bus pins:

  • Pin 11: MOSI
  • Pin 12: MISO
  • Pin 13: SCK
    These 3 Pins also connect to the ICSP connector on Uno. The WiFi Shield connects to these signals through the ICSP connector, and not through the above Pins. But they are in use. The SPI Library controls this bus. The code examples have #include <SPI.h> statements, but leaving this statement out of my code does not seem to break anything.
    Q: Is the include statement still needed, or is it part of the IDE default?
    Q: Is this data path used by both modules on the Shield, or only the WiFi module?

Finally:

  • Pin 7: Wifi Handshake (Int1 on WiFi schematic)
  • Pin 9: A free buffered LED (Thanks, Massimo)
    "L9 is there for “historical reasons” but it’s not used. we’ll update that in the future."

The USB serial monitor connection uses Pin 0 and Pin 1. The modules on the WiFi Shield do not use these pins, but the Uno does. Serial.begin(baud_rate) sets these pins up for the USB monitor connection.
Q: Can this serial connection interface with more devices, or are they dedicated to the USB connector? If expandable, please point me to documentation.

In addition to Pin 9, pins 2, 3, 5, 6, and 8 are available for hacking. Also, A0 through A5 map to Pins 14 through 19 for use as digital interfaces, by using the same digitalWrite(Pin, level) instruction (after appropriate setup).

Please correct any errors. I plan to have my soldering iron out soon :slight_smile:

Regards,
Rudy