Using the MC145158 PLL Frequency Synthesizer

Posted on Feb 5, 2014

The Motorola MC145158 is a dual-modulus, serial-input PLL frequency synthesizer which is commonly used in older Motorola cellular phones. Refer to the MC145158's datasheet for the nitty-gritty technical details. The MC145158 is no longer manufactured, but it does pop up from time-to-time in surplus electronic stores. Digi-Key used to carry it, part number MC145158DW2-ND. The Fujitsu equivalent is the MB87001A, which is very common in old Japanese-manufactured (Uniden, Toshiba, etc.) cellular phones. The programming of the MB87001A is the same as the MC145158, but the technical specs to the MB87001A are slightly different. The maximum input frequency for the MC145158 is only around 20 MHz when run at +9 VDC. It drops to around 15 MHz at +5 VDC. The R-Counter reference frequency divider range is between 3 and 16,383. The N-Counter can be between 3 and 1,023. The A-Counter dual-modulus range is between 0 and 127. When using an external dual-modulus prescaler set to /64 (divide-by-64), such as a Motorola MC12022 or Fujitsu MB501, don't exceed a value of 63 for the A-Counter.

Using the MC145158 PLL Frequency Synthesizer

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The MC145158 is designed to be programmed via a microcontroller using a standard serial-input data stream. The MC145158 has pins for the shift clock (CLK, pin 9), serial data input (DATA, pin 10), and latch enable (ENB, pin 11). These three lines control how and when the PLL is programmed. Once programmed, all the counter's values will remain programmed until power is removed from the circuit. Also, the counters must be programmed Most Significant Bit (MSB) first. A logic high on this pin latches the data from the shift register into the reference divider or /N, /A latches depending on the control bit. The reference divider latches are activated if the control bit is at a logic high and the /N, /A latches are activated if the control bit is at a logic low. A logic low on this pin allows the user to change the data in the shift registers without affecting the counters. ENB is normally low and is pulsed high to transfer data to the latches. What this means, in English, is that to program the counter data into the MC145158, you need to set the voltage on the DATA pin to +5 volts for a logic 1, and 0 volts (ground) for a logic 0. You'd then raise the CLK pin to +5 volts, from it's initial value of 0, then quickly bring it back to 0 volts. Do this 15 times to load the R-Counter value (14 bits, plus one control bit). When finished, raise the ENB pin to +5 volts, from it's initial value of 0, then quickly bring it back...

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