MC145170-2 查看數據表（PDF） - Motorola => Freescale

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MC145170-2

PLL Frequency Synthesizer with Serial Interface

Motorola => Freescale 

Freescale Semiconductor, Inc.

Pin Connections

ENB

Active-Low Enable Input (Pin 6)

This pin is used to activate the serial interface to allow the transfer of data to/from the device. When ENB

is in an inactive high state, shifting is inhibited, Dout is forced to the high-impedance state, and the port is

held in the initialized state. To transfer data to the device, ENB (which must start inactive high) is taken

low, a serial transfer is made via Din and CLK, and ENB is taken back high. The low-to-high transition on

ENB transfers data to the C, N, or R register depending on the data stream length per Table 7.

NOTE: Transitions on ENB must not be attempted while CLK is high. This puts the device out of

synchronization with the microcontroller. Resynchronization occurs when ENB is high and CLK is low.

This input is also Schmitt-triggered and switches near 50% of VDD, thereby minimizing the chance of

loading erroneous data into the registers. See the last paragraph of Din for more information.

Dout

Three-State Serial Data Output (Pin 8)

Data is transferred out of the 16-1/2-stage shift register through Dout on the high-to-low transition of CLK.

This output is a No Connect, unless used in one of the manners discussed below.

Dout could be fed back to an MCU/MPU to perform a wrap-around test of serial data. This could be part of

a system check conducted at power up to test the integrity of the system's processor, PC board traces,

solder joints, etc.

The pin could be monitored at an in-line QA test during board manufacturing.

Finally, Dout facilitates troubleshooting a system and permits cascading devices.

3.2 Reference Pins

OSCin/OSCout

Reference Oscillator Input/Output (Pins 1, 2)

These pins form a reference oscillator when connected to terminals of an external parallel-resonant crystal.

Frequency-setting capacitors of appropriate values as recommended by the crystal supplier are connected

from each pin to ground (up to a maximum of 30 pF each, including stray capacitance). An external

feedback resistor of 1.0 to 5.0 MΩ is connected directly across the pins to ensure linear operation of the

amplifier. The required connections for the components are shown in Figure 11.

5 MΩ is required across the OSCin and OSCout pins in the ac-coupled case (see Figure 9 or alternate circuit

Figure 10). OSCout is an internal node on the device and should not be used to drive any loads (i.e.,

OSCout is unbuffered). However, the buffered REFout is available to drive external loads.

The external signal level must be at least 1 Vpp; the maximum frequencies are given in the Loop

Specifications table. These maximum frequencies apply for R Counter divide ratios as indicated in the

table. For very small ratios, the maximum frequency is limited to the divide ratio times 2 MHz. (Reason:

the phase/frequency detectors are limited to a maximum input frequency of 2 MHz.)

If an external source is available which swings virtually rail-to-rail (VDD to VSS), then dc coupling can be

used. In the dc-coupled case, no external feedback resistor is needed. OSCout must be a No Connect to

avoid loading an internal node on the device, as noted above. For frequencies below 1 MHz, dc coupling

must be used. The R counter is a static counter and may be operated down to dc. However, wave shaping

by a CMOS buffer may be required to ensure fast rise and fall times into the OSCin pin. See Figure 25.

Each rising edge on the OSCin pin causes the R counter to decrement by one.

MOTOROLA

MC145170-2 Technical Data

11

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