Casio HBX-100 'PC-Unite' databank watch
I expected this unit to be built with some serious minaturisation techniques - chip-on board assembly and microscopic components. I was rather surprised to see that apart from the main CPU, very conventional assembly was in fact used. I suspect this may have been to reduce development costs for what is probably a relatively low-volume product for Casio. Maybe future versions will be more miniaturised, reducing the overall size. I was also surprised that it used a flash device for data storage rather than battery-backed static RAM. Again this may have been due to availability of standard parts, the low volumes not justifying custom chips.
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Grey circles on left are rubber buttons (conductive rubber pads on rear).
Chip below it is a 16kbyte serial flash memory, Xicor X24F128. This presents some interesting questions -
the watch specs state that memory capacity is approximately 8K, so what is the other 8K
used for ? As it's a serial device, it can't be code, unless the CPU has a large on-chip
RAM to copy it to. Also, as it's a flash device, and therefore nonvolatile, why does the
watch trash the stored data when you change the battery and reset it? Unfortunately
my device programmer doesn't support this device, otherwise I would have read the
Black object on right is the infra-red IRDA transceiver. I was surprised to see one of these used instead of a smaller descrete infra-red LED/Receiver pair, which could have been a lot smaller.
Note the circular solder-bridgeable pad pair to the left of the second
grey button from the top. When delving inside things you often find these factory-settable
links. Of course I had to try linking it.... When this pad is linked, the PC software
reports that the watch type is unrecognised, and the text entry uses only Japanese
Going round the board clockwise starting at 12 O'clock....
Inductor for switching power supply chip (top right), I think this is the supply for the infra-red transceiver. I suspect this chip is one of the Torex range
Bottom right - crystal (probably 32.768KHz) for timekeeping (obscured by black felt pad stuck to the top) , with fine-adjust trimmer above-right.
Bottom centre - 3.68MHz Ceramic resonator main CPU clock. The CPU will spend most of its time asleep or running at the lower watch crystal frequency to save power, and use this high-frequency clock when it needs to do anything more demending than show the time.
Chip at top-left (Panasonic M803 83) drives the electroluminescent
backlight. It uses the round coil above it to step up the 3v battery to the high voltage
(typically 50-100V) required by the backlight.
This is the PCB from the PAD-1 PC to IR interface supplied with the watch.
I suspect this is a standard OEM product which has been badged by Casio.It uses a standard Hewlett-Packard IRDA interface chip, pluse some standard logic devices to interface the PC RS-232 port to an IRDA transceiver.
The packaging warns that the interface will not work on a laptop - this is
because it takes its power from the RS-232 port, and laptops tend to have less power
available from serial ports due to the low-power circuitry they typically use to generate
the RS-232 voltage levels.