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Project: 0xc0ffee

Inside the AEG CaFamosa 80

Bits and pieces

After some work, we could have a close look at the electronics inside the CaFamosa80. Now that I have a digital camera, I will take and publish some photos as soon as I open the machine again.

There are two PCBs visible in the machine's front: One (which we are concentrating on) carrying the buttons and LEDs the user uses, and another one, built into the casing, possibly carrying the high power electronics, such as switches for motors, pumps, and heatings.

The front PCB carries one quite large and some smaller ICs, marked as follows:

Large:
    UCHIE 101-4
    TOPTRONIC
    HD6433212L02P
    1M4

Small, near the service connector:
    M74HC14B1
    W991LC141

Small, somewhere else:
    ULN2803A
    W993R013S

The large IC is a H8/3212 microcontroller, made by Hitachi, and obviously programmed by Toptronic (We have found that company and asked for details of the circuitry, but they did not want to tell anything). It contains an 8-bit CPU (running at 16 MHz), 16 KB ROM, and 512B RAM. Plus, it does contain one serial communication interface, and 16 outputs delivering up to 10 mA (which is considered "high-current" by Hitachi). The serial interface supports speeds from 300 to 38400 bit/sec.

The M74HC14B1 is a high speed CMOS hex Schmitt inverter. In a bit, we will see what it is used for here, and why it is especially interesting.

The ULN2803A is designated a "octal peripheral driver array". I will also come back to that later.

Board layout

As we originally wanted to find out how the service port works, I now took a closer look at the connectors leading to that port, and on the PCB design beneath them.

The interesting parts of the board looked as if they were designed like my poor ASCII art pictures. Please note: I am using European symbols here. Please look them up, I had to learn the American ones, too. The colors mentioned are the colors leading out to the service interface.

            ,____,
 (ylo)-----o--|____|---||------o-----(or)
           |     ,-------------'
           |     |
         +-O-O-O-O-O-O-O-+
         |     M74HC14B1 |
         |@@             |
         |     W991LC141 |
         +-O-O-O-O-O-O-O-+

Of course, there were other connections, which I did not draw here. When we look up a datasheet for that CMOS inverter, we find that pin 14 (connected directly to the yellow cable of the service interface) is to be connected to Vcc (+5V). So the strong suspicion came to us that the yellow cable is just a +5V supply for whatever device is connected to the machine's service port. This is backupped by the unused service connector pin (*) used to separate this supply line from the data lines.

Pin 11 of the inverter IC is an input. Signals coming in here are inverted and sent out (at CMOS voltage level) through pin 10.

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Last page update: 2005-10-24