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MC145202F Fiches technique(PDF) 10 Page - Motorola, Inc |
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MC145202F Fiches technique(HTML) 10 Page - Motorola, Inc |
10 / 24 page MC145202 MOTOROLA 10 OUTPUT A Configurable Digital Output (Pin 16) OUTPUT A is selectable as fR, fV, Data Out, or Port. Bits A22 and A23 in the A register control the selection; see Figure 15. If A23 = A22 = high, OUTPUT A is configured as fR. This signal is the buffered output of the 13–stage R counter. The fR signal appears as normally low and pulses high. The fR signal can be used to verify the divide ratio of the R counter. This ratio extends from 5 to 8191 and is determined by the binary value loaded into bits R0–R12 in the R register. Also, direct access to the phase detectors via the REFin pin is al- lowed by choosing a divide value of 1 (see Figure 16). The maximum frequency at which the phase detectors operate is 2 MHz. Therefore, the frequency of fR should not exceed 2 MHz. If A23 = high and A22 = low, OUTPUT A is configured as fV. This signal is the buffered output of the 12–stage N counter. The fV signal appears as normally low and pulses high. The fV signal can be used to verify the operation of the prescaler, A counter, and N counter. The divide ratio between the fin input and the fV signal is N × 64 + A. N is the divide ratio of the N counter and A is the divide ratio of the A counter. These ratios are determined by bits loaded into the A register. See Figure 15. The maximum frequency at which the phase detectors operate is 2 MHz. Therefore, the fre- quency of fV should not exceed 2 MHz. If A23 = low and A22 = high, OUTPUT A is configured as Data Out. This signal is the serial output of the 24–1/2–stage shift register. The bit stream is shifted out on the high–to–low transition of the CLK input. Upon power up, OUTPUT A is automatically configured as Data Out to facilitate cascading devices. If A23 = A22 = low, OUTPUT A is configured as Port. This signal is a general–purpose digital output which may be used as an MCU port expander. This signal is low when the Port bit (C1) of the C register is low, and high when the Port bit is high. OUTPUT B Open–Drain Digital Output (Pin 15) This signal is a general–purpose digital output which may be used as an MCU port expander. This signal is low when the Out B bit (C0) of the C register is low. When the Out B bit is high, OUTPUT B assumes the high–impedance state. OUTPUT B may be pulled up through an external resistor or active circuitry to any voltage less than or equal to the poten- tial of the VPD pin. Note: the maximum voltage allowed on the VPD pin is 5.5 V. Upon power–up, power–on reset circuitry forces OUTPUT B to a low level. REFERENCE PINS REFin and REFout Reference Input and Reference Output (Pins 20 and 1) Configurable pins for a Crystal or an External Reference. This pair of pins can be configured in one of two modes: the crystal mode or the reference mode. Bits R13, R14, and R15 in the R register control the modes as shown in Figure 16. In crystal mode, these pins form a reference oscillator when connected to terminals of an external parallel–reso- nant crystal. Frequency–setting capacitors of appropriate values, as recommended by the crystal supplier, are con- nected from each of the two pins to ground (up to a maximum of 30 pF each, including stray capacitance). An external re- sistor of 1 M Ω to 15 MΩ is connected directly across the pins to ensure linear operation of the amplifier. The required con- nections for the components are shown in Figure 9. To turn on the oscillator, bits R15, R14, and R13 must have an octal value of one (001 in binary, respectively). This is the active–crystal mode shown in Figure 16. In this mode, the crystal oscillator runs and the R Counter divides the crystal frequency, unless the part is in standby. If the part is placed in standby via the C register, the oscillator runs, but the R counter is stopped. However, if bits R15 to R13 have a value of 0, the oscillator is stopped, which saves additional power. This is the shut–down crystal mode (shown in Figure 16) and can be engaged whether in standby or not. In the reference mode, REFin (Pin 20) accepts a signal from an external reference oscillator, such as a TCXO. A sig- nal swinging from at least the VIL to VIH levels listed in the Electrical Characteristics table may be directly coupled to the pin. If the signal is less than this level, ac coupling must be used as shown in Figure 8. Due to an on–board resistor which is engaged in the reference modes, an external bias- ing resistor tied between REFin and REFout is not required. With the reference mode, the REFout pin is configured as the output of a divider. As an example, if bits R15, R14, and R13 have an octal value of seven, the frequency at REFout is the REFin frequency divided by 16. In addition, Figure 16 shows how to obtain ratios of eight, four, and two. A ratio of one–to–one can be obtained with an octal value of three. Upon power up, a ratio of eight is automatically initialized. The maximum frequency capability of the REFout pin is listed in the Loop Specifications table for an output swing of 1 V p–p and 20 pF loads. Therefore, for higher REFin fre- quencies, the one–to–one ratio may not be used for this magnitude of signal swing and loading requirements. Like- wise, for REFin frequencies above two times the highest rated frequency, the ratio must be more than two. The output has a special on–board driver that has slew– rate control. This feature minimizes interference in the ap- plication. If REFout is unused, an octal value of two should be used for R15, R14, and R13 and the REFout pin should be floated. A value of two allows REFin to be functional while disabling REFout, which minimizes dynamic power consumption. LOOP PINS fin and fin Frequency Inputs (Pins 11 and 10) These pins are frequency inputs from the VCO. These pins feed the on–board RF amplifier which drives the 64/65 pre- scaler. These inputs may be fed differentially. However, they are usually used in a single–ended configuration (shown in Figure 7). Note that fin is driven while fin must be tied to ground via a capacitor. Motorola does not recommend driving fin while terminating fin because this configuration is not tested for sensitivity. The sensitivity is dependent on the frequency as shown in the Loop Specifications table. |
Numéro de pièce similaire - MC145202F |
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Description similaire - MC145202F |
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