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DALLAS realtime clock interface

I wanted to add a realtime clock to my SAM other then the hard to get realtime clock chip used in the sambus and discovered the realtime clock chip from dallas semiconductors which has two big advantages: All clock components inclusive a backup battery are in a single package so implementation is easy, and this clock can be found on PC motherboards which makes it easy to get.

The Dallas clock can operate in INTEL mode and MOTOROLA mode. In order to reduce the chip count I choose to use the MOTOROLA mode.

My original design of the DALLAS clock was based on integration with the SAM's Comms interface (In which I already build my EDDAC interface). But to make it function as a stand alone interface a 74LS138 address decoder was added.


DALLAS Clock Schematic


I recommend to fit the clock chip in a 24 pin DIL socket. IC 2 and the ceramic capacitor can be fitted inside the DIL socket.


The Dallas Clock is supported by B-DOS and also several utilities by Martijn Groen.


1DS 12887 (DS 1287 will do also)
122 nF ceramic capacitor
122 uF/16V Electrolitic capacitor *
* Not required when clock is build inside Comms interface.


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