Abstract
Up to this point we have mainly concentrated on how the software has interacted with the processor’s internal registers and Data memory. Now, as a prelude to how the MCU relates to its internal peripheral devices and hence monitors and controls its external environment, i.e. the real world outside its pins, we need to look at external support issues, such as power supply requirements, clocking and resetting.
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The PIC16F83 is identical to the PIC16F84 but has 50% less Program memory and 36 instead of 68 file registers. The latter is currently available as the PIC16F84A with minor enhancements.
The main exceptions are the input to MCLR (Master CLeaR) which requires a voltage VIH of 0.85Vpp before coming out of reset, and 0.7Vpp for any oscillator driving the OSC1 input as an external clock.
This is why most current microprocessors used as the PC CPU, such as the Intel Pentium III, are powered at under 3 V rather than the standard 5 V of older devices.
The older PIC16F83/4 comes in two speed selections, namely 4MHz (PIC16F8X-04) and 10 MHz (PIC 16F8X-10).
If using a TTL-compatible oscillator then a pull-up resistor may be needed to ensure a high enough VIH.
The area of Program memory beyond the user Program store space belongs to the special test/configuration memory space 2000h-3FFFh which can be accessed only during external programming.
Remember the byte address 400Eh is twice the byte address equivalent 2007h and words are presented least-significant byte first.
Even such close relatives as the PIC16C74 and PIC16C74A/B have differing fuse dispositions, so it is essential to use the exact correct header file!
kHz crystal oscillators have a typical start-up time of 1–2 seconds. Crystal oscillators ≥ 100 kHz have a typical start-up time of less than 10–20 ms and ceramic resonators are typically less than 1 ms. Times are voltage dependent.
Uncharacteristically the PIC16C71 becomes the PIC16C711.
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© 2001 Springer-Verlag London
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Katzen, S. (2001). The Real World. In: The Quintessential PIC Microcontroller. Computer Communications and Networks. Springer, London. https://doi.org/10.1007/978-1-4471-3704-7_10
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DOI: https://doi.org/10.1007/978-1-4471-3704-7_10
Publisher Name: Springer, London
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