unicore UFirebird II, Reference Design, Page: 9 / 15

4 Attention UC-06-C21 EN R1.0
2.2 Reset Signal
UC6580 supports system reset. The reset signal is active low and the active time should
be no less than 5 ms.
2.3 RTC
RTC is usually driven by an on-chip 32.768 kHz oscillator, which needs to be connected
to an external 32.768 kHz crystal.
Instead of this, UC6580 supports directly inputting RTC_I with an external 32.768 kHz
digital clock signal. In this situation, make sure that the signal amplitude is less than
1.98 V, otherwise it may cause damage to the chip.
In addition to the general rules of RTC layout and routing, you should pay special
attentions to:
 Have a complete reference GND under the chip and the RTC crystal.
 The RTC crystal shall be placed as close to the chip as possible, and there shall be
no other devices between the two;
 Devices, signals, wiring, etc. with high power or strong interference should be
avoided around RTC crystal;
 It is recommended to do ground shields for the relevant circuits of RTC.