Abstract
Understanding the hardware architecture of the core and its configuration is key to effective utilization of its hosted array of peripheral interface modules. Where necessary, the more feature-rich PIC18FXX20 devices are used as exemplars.
This first chapter of Part III, which primarily deals with the interaction of the microcontroller with the outside world, looks at the hardware of the PIC18 core and how the running environment is set-up. Topics covered include power supply issues, static and dynamic power dissipation, reset processes, clocking the processor, including Run, Sleep and Idle modes with integral and external oscillators, and the various reset mechanisms, including brown-out.
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- 1.
The PIC18F1320 is identical but with double the Program store size at 2 kwords.
- 2.
The main exceptions are oscillator I/O and RC[4:3] pins.
- 3.
This is why most current microprocessors used as the PC’s CPU, such as the Intel Pentium IV, are powered at under 3 V rather than the standard 5 V of older devices.
- 4.
The PIC18FXXK subfamily has a maximum clocking frequency of 64 MHz.
- 5.
If using a TTL-compatible oscillator, then a pull-up resistor may be needed to ensure a high enough V IH .
- 6.
Locations h’3FFFE:F’ are read-only Device registers, holding the part number and hardware version details. Eight locations h’20000–20007’ are designated ID, where the user can store code identification data; such as company and version information.
- 7.
Older versions of the assembler required the programmer to specify each Configuration register when listing the various options. For instance, config config4l, XINST=ON.
- 8.
If the Watchdog timer is enabled, the INTRC oscillator continues to operate, as does the Secondary oscillator if Timer 2 requires it.
- 9.
In some family members, such as the PIC18F1220, INTRC and INTOSC are linked.
- 10.
The SCS0 bit is don’t care for our exemplar devices, but it is recommended that it should be 0 for compatibility with future device enhancements.
- 11.
The PIC24 family extend this approach with Doze modes. These allow peripheral processing at full speed and core execution at a reduced rate. In addition, each Peripheral module can be opted out of the Idle modes.
- 12.
32 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.
- 13.
The term is from the same phenomena in the mains supply that causes the lights to dim and give a brownish hue to the surroundings!
- 14.
If the supply falls below 0.7 V, then a Power-on Reset will occur.
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© 2010 Springer-Verlag London Limited
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Katzen, S. (2010). The Real World. In: The Essential PIC18® Microcontroller. Computer Communications and Networks. Springer, London. https://doi.org/10.1007/978-1-84996-229-2_10
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DOI: https://doi.org/10.1007/978-1-84996-229-2_10
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