Copyright © 2015 Robot Circuits, LLC
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RCAT-1A Rev A3 Designer’s manual
Serious Power for the Serious Designer
System Clock
The onboard 16MHz crystal provides the CPU timing reference.
Schematic
Figure 11
Notes
Although rare, it is possible to “brick” the ATMega™ chip by improperly setting clock values in the programming
apparatus and even sometimes, again, very rarely, as a result of improper voltages or signals being applied to
numerous ports on the CPU. When that occurs, it is necessary to provide an externally generated clock to the
CPU in order to recover. There are plenty of how-tos available online in the event you should brick your board.
But one thing is always necessary – to inject an external clock into the XTAL1 input of the CPU. For this reason,
JP1 is provided so that you can remove the jumper and connect your external clock to the CPU. Hopefully you
will never need this, but in the event it happens, at least you won’t have to unsolder the crystal just to recover
your board.
Extended Static RAM
Schematic
Figure 12
