SX User’s Manual Rev. 3.1 142 © 2000 Scenix Semiconductor, Inc. All rights reserved. www.scenix.com Chapter 4 Clocking, Power Down, and Reset The device initialization routine can determine the Port B pin that caused the wakeup to occur by
reading the WKPND_B register, as described in Section 4.4.1. 4.5.4 Brown-Out Reset When the supply voltage to the SX device drops below a specified value but remains above zero volts,
it is called a “brown-out” condition. The SX device has a brown-out detection circuit that puts the
device into the reset state when a brown-out occurs, and allows the device to re-start when the brown-
out condition ends. This feature prevents the device from producing abnormal results when the supply
voltage falls to unreliable levels. The  brown-out  threshold  voltage  is  programmable  through  the  BOR1:BOR0  bits  in  the  FUSEX
register. If the supply voltage drops below this level but remains above zero, the brown-out circuit
holds the SX device in the reset state. When the voltage rises above this threshold, the device starts
operating again, starting at the reset address (the highest memory address). You can optionally disable the brown-out detection circuit by setting the BOR0 and BOR1 bits to 1 in
the FUSEX word register (a register programmed along with the instruction memory). In that case, the
device will still operate below the brown-out threshold voltage, but will produce unreliable results if
the supply voltage falls too low. 4.5.5 Watchdog Timeout A Watchdog timeout occurs if the Watchdog circuit is enabled and the Watchdog timer overflows. This
feature provides an escape mechanism from an infinite loop or other abnormal program condition.
When a Watchdog timeout occurs, it resets the device just like assertion of the MCLR input. 4.5.6 MCLR Input Signal (Master Clear Reset) A reset occurs whenever the MCLR (Master Clear Reset) input pin goes low. The device is held in the
reset state as long as the MCLR pin is held low. When the input goes high, the program jumps to the
reset address (the highest memory address). If you do not intend to use the MCLR pin as a hardware
reset input,  you should connect it  together with the  power  supply pin (Vdd) or to a  power-on RC
network, as described in Section 4.5.2.