We have already met RCON, as its MSB is the interrupt IPEN bit. This information is provided through the RCON register, whose bits indicate what type of reset has occurred most recently. In certain circumstances this can be very valuable, say if the Watchdog Timer has timed out. Now we can find out why we were forced into reset. Therefore, coming out of the Reset condition is not the completely fresh start that it is with simple microcontrollers. These are Stack over- or under-flow, Brown-out (already seen in the 16F873A) and use of the instruction reset.īesides adding further sources of reset, the 18 Series goes beyond this in an interesting way, by providing some history of what the source of reset was. The 18FXX20 controllers have a reset structure built directly on the model of Figure 2.10, with just a few extra sources of reset. In Section 2.8 of Chapter 2 we explored the reset circuitry of a simple PIC microcontroller, the 16F84A. The data shows that its maximum clock frequency at minimum supply voltage is 4 MHz. The low-power device cannot, however, run at full speed at the lower voltage.
This shows that the 18LFXX20 devices can operate with a supply from 2.0 to 5.5 V, and the 18FXX20 from 4.2 to 5.5 V.
The supply voltage requirements of the 18LFXX20 and the 18FXX20 are shown in Figure 13.13. Tim Wilmshurst, in Designing Embedded Systems with PIC Microcontrollers (Second Edition), 2010 13.8 Power supply and reset 13.8.1 Power supply
