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Pushpin Computing
Responsive Environments Group

Cygnal C8051F016 Processing Module Assembly

The following provides step-by-step instruction for assembling a complete processing module from its constituent parts.

This is the uncut printed circuit board as it comes from the factory. It consists of four separate boards, one of which is the processing module board, that must be cut apart and whose edges must be sanded down. A sheet metal cutter and a grinder work well for these purposes.
This is the top view of the processing module board after it has been cut from the original printed circuit board and had its edges sanded, but before any parts have been added to it. The top is here defined to be the side on which the expansion connector resides. It is also the side containing the Cygnal microprocessor.
This is the bottom view of the processing module board before any parts have been added. The bottom is here defined to be the side on which the communications module connector resides.
The microprocessor is the very first part to add to the top of the micro. This is easily the most difficult and time-consuming step. A separate tutorial will be posted shortly explaining how to do this.
If the microprocessor was added to the board with the aid of flux, it is necessary to remove any remaining flux before adding other parts. This is because flux is somewhat sticky and particles of metal can easily get stuck, possibly causing a short between pins. Also, although flux isn't conductive, it does have a different dielectric constant than air, which will affect some high-speed applications. Any mild solvent (soap for example) used under running water with a fine-toothed brush will suffice to remove excess flux. Brush vigorously. Check the board under a microscope for spots you may have missed.
The 25-pin receptacle should be soldered to the board after the microprocessor has been soldered and the board cleaned of excess flux and dried. The direction the receptacle faces is important, as one side has 12 pins and the other 13 pins. To begin with, solder down a couple of pins on each side of the receptacle and then check to be sure the connector is flush with the board. Once it is flush, solder the remaining pins and the mechanical supports on the two ends. Although the supports do not make any electrical connections on the receptacle, they are soldered to ground and power on the board.
After soldering on the receptacle, examine the pins under a magnifier and be sure they do not move when you apply pressure with the tweezers. Do this now before adding other parts so that you have full access to all the pins. (The crystal blocks several of the pins otherwise).
The third part to add to the top of the processing module printed circuit board is the 22.118MHz crystal. The crystal package has four pins, but only two of them are electrically active; the other two are provided for mechanical support. One of the inactive pins must be removed due to the compactness of the processing layer PCB design. The crystal's footprint on the PCB reflects this fact. The half-circle notch on one end of the crystal package should be facing the 25-pin receptacle.
Once the crystal has been attached, check for excess solder. The capacitance of the electrically active pins will effect crystal performance, so be sure to use only the minimum solder needed for mechanical support.
Solder on the 4.7uF 0805 footprint capacitor. The polarity of the capacitor is not important. 0805 designates the physical size of the capacitor. Unfortunately, there are no markings on the capacitor itself to indicate that it is 4.7uF (uF is short for microfarad).
This is an image of the top of the processing module board after the 4.7uF 0805 footprint capacitor has been added.
Solder on the red 0603 surface mount red LED. Be sure it is facing the right way, otherwise it won't work. The very small square embedded in the LED should be on the side closest to the microprocessor. Note that if using a color other than red, the polarity of the LED is most likely reversed. Presumably, this is an artifact of the manufacturing process used for this specific brand of LED.
This is an image of the top side of the processing module board with all its components in place.
The four connecting posts protruding from the corners of the bottom side of the processing module board are retrofitted posts from DIP sockets. Use wire clippers to cut away the plastic and remove the pins from the DIP socket.
The smaller ends of the posts should be clipped either before or after being soldered in place. The two posts located under the 25-pin receptacle should have their smaller ends clipped short before they are soldered in so as to not be obstructed by the receptacle above. The length of the clipped pin ends should be only slightly less than the thickness of the printed circuit board. These four posts provide mechanical support and are all electrically active (power, ground, transmit, and receive).
The next part to solder to the bottom of the processing module is the 9-pin receptacle that is used to connect down to a communications module. The alignment of this part is crucial to how the communication and processing modules fit together.
Once the 9-pin receptacle has been soldered to the board, check all the connections under a microscope.
Select a 0603 footprint 10kOhm resistor. 0603 is the physical size of the resistor. The resistor's resistance should be printed on the resistor as a three-digit code. The actual resistance value in Ohms is the number composed of the two left-most digits times ten raised to the right-most digit. Thus, 10kOhms is represented by the code 103.
Solder on the 10kOhm resistor. This resistor acts as a pull-up resistor on the active-low reset pin and prevents the microprocessor from continually resetting itself.
Solder on two 18pF capacitors. Due to the cramped board layout, care must especially be taken here to avoid shorting two separate electrical nets. As was the case with the 4.7uF capacitor, the polarity of the 18pF capacitors is not important
This image shows the completed bottom side of the processing module after the final part, the 150Ohm (resistor code 151) 0603 footprint resistor, has been placed.
Test the completed Pushpin processing module by downloading a simple program you know works.

Last Updated: 01-DEC-2004
MIT Media Laboratory