Contents:
Programming voltage input. Digital input. Oscillator crystal input or external clock source input. External clock source input. Always associated with pin function OSC1. Oscillator crystal output. Connects to crystal or resonator in Crystal Oscillator mode.
Analog input 0. Analog input 1. Analog input 2. Analog comparator reference output. Analog input 3. Timer0 external clock input. Comparator 1 output. Analog input 4. SPI slave select input. Comparator 2 output. PORTB can be software programmed for internal weak pull-ups on all inputs.
Analog input External interrupt 0. SPI data in. External interrupt 1. Analog input 8. External interrupt 2. Analog input 9. Interrupt-on-change pin. Timer1 oscillator output. Timer1 oscillator input. SPI data out. SPP chip select control output. Streaming Parallel Port data. Analog input 5. SPP clock 1 output.
Analog input 6. SPP clock 2 output.
DSB. PIC18F/// Data Sheet. 28/40/Pin High- Performance,. Enhanced Flash USB Microcontrollers with nanoWatt Technology . PIC18F/// Special Microcontroller Features: .. products meet the specification contained in their particular Microchip Data Sheet.
Analog input 7. SPP output enable output. In-Circuit Debugger clock. ICSP programming clock. In-Circuit Debugger data. ICSP programming data. Enable pin device emulation when connected to VSS. NC — 13 — — — No Connect. NOTES: The addi- tion of the USB module, with its unique requirements for a stable clock source, make it necessary to provide a separate clock source that is compliant with both USB low-speed and full-speed specifications.
Since it is driven from the primary clock source, an additional system of prescalers and postscalers has been added to accommodate a wide range of oscillator frequencies. An overview of the oscillator structure is shown in Figure Other oscillator features used in PIC18 enhanced microcontrollers, such as the internal oscillator block and clock switching, remain the same. They are discussed later in this chapter. As Configuration bits, these are set when the device is programmed and left in that configuration until the device is reprogrammed.
Its use is discussed in Section 2. Its use is described in Section 2. In contrast with pre- vious PIC18 enhanced microcontrollers, four of these modes involve the use of two oscillator types at once.
Thus, the USB module must be clocked from the primary clock source; however, the microcontroller core and other peripherals can be separately clocked from the secondary or internal oscillators as before. Fortunately, the microcontroller and other peripherals are not required to run at this clock speed when using the primary oscillator.
There are numerous options to achieve the USB module clock requirement and still provide flexibil- ity for clocking the rest of the device from the primary oscillator source. These are detailed in Section 2. Figure shows the pin connections. The oscillator design requires the use of a parallel cut crystal.
An external clock may also be used when the micro- controller is in HS Oscillator mode. These capacitors were tested with the resonators listed below for basic start-up and operation. These values are not optimized. Different capacitor values may be required to produce acceptable oscillator operation. The user should test the performance of the oscillator over the expected VDD and temperature range for the application. See the notes following Table for additional information.
Resonators Used: 4. These capacitors were tested with the crystals listed below for basic start-up and operation. See the notes following this table for additional information. There is no oscillator start-up time required after a Power-on Reset or after an exit from Sleep mode. This signal may be used for test purposes or to synchronize other logic.
Figure shows the pin connections for the EC Oscillator mode. This is provided specifically for USB applications with lower speed oscillators and can also be used as a microcontroller clock source. It is designed to produce a fixed 96 MHz reference clock from a fixed 4 MHz input.
The output can then be divided and used for both the USB and the microcontroller core clock.
Because the PLL has a fixed frequency input and output, there are eight prescaling options to match the oscillator input frequency to the PLL. There is also a separate postscaler option for deriving the microcontroller clock from the PLL. This allows the USB peripheral and microcontroller to use the same oscillator input and still operate at different clock speeds. The choice of the USB clock source is determined by the particular internal oscillator mode. There are four distinct modes available: 1. The tuning sensitivity is constant throughout the tuning range.
Code execution continues during this shift.
There is no indication that the shift has occurred. The INTSRC bit allows users to select which internal oscillator provides the clock source when the 31 kHz frequency option is selected. This is covered in greater detail in Section 2. However, this frequency may drift as VDD or tempera- ture changes, which can affect the controller operation in a variety of ways.
Tuning the INTOSC source requires knowing when to make the adjustment, in which direction it should be made and in some cases, how large a change is needed. When using the EUSART, for example, an adjustment may be required when it begins to generate framing errors or receives data with errors while in Asynchronous mode. Framing errors indicate that the device clock frequency is too high; to adjust for this, decrement the value in OSCTUNE to reduce the clock frequency.
On the other hand, errors in data may sug- gest that the clock speed is too low; to compensate, increment OSCTUNE to increase the clock frequency. It is also possible to verify device clock speed against a reference clock. Two timers may be used: one timer is clocked by the peripheral clock, while the other is clocked by a fixed reference source, such as the Timer1 oscillator.
Both timers are cleared but the timer clocked by the reference generates interrupts. When an interrupt occurs, the internally clocked timer is read and both timers are cleared. If the internally clocked timer value is greater than expected, then the internal oscillator block is running too fast. Finally, a CCP module can use free-running Timer1 or Timer3 , clocked by the internal oscillator block and an external event with a known period i.
When the second event causes a capture, the time of the first event is subtracted from the time of the second event. Since the period of the external event is known, the time difference between events can be calculated. If the measured time is much greater than the calcu- lated time, the internal oscillator block is running too fast; to compensate, decrement the OSCTUNE register. If the measured time is much less than the calculated time, the internal oscillator block is running too slow; to compensate, increment the OSCTUNE register.
Oscillator module is running at the calibrated frequency. This may require some forethought in selecting an oscillator frequency and programming the device. The full range of possible oscillator configurations compatible with USB operation is shown in Table It is divided by 4 to produce the actual 6 MHz clock.
This restriction does not apply if the microcontroller clock source is the secondary oscillator or internal oscillator block.