CD4059A-MIL CMOS 可编程 N 分频计数器

CD4059 standard "A" Series types are divide-by-N down-counters that can be programmed to divide an input frequency by any number "N" from 3 to 15,999. The output signal is a pulse one clock-cycle wide occurring at a rate equal to the input frequency divided by N. This single output has TTL drive capability. The down-counter is preset by means of 16 jam inputs.

The three Mode-Select Inputs Ka, Kb, and Kc determine the modulus ("divide-by" number) of the first and last counting sections in accordance with the truth table shown in Table 1. Every time the first (fastest) counting section goes through one cycle, it reduces by 1 the number that has been preset (jammed) into the three decades of the intermediate counting section and into the last counting section, which consists of flip-flops that are not needed for operating the first counting section. For example, in the 2 mode, only one flip-flop is needed in the first counting section. Therefore the last counting section has three flip-flops that can be preset to a maximum count of seven with a place value of thousands. If 10 is desired for the first section, Ka is set 1, Kb to 1, and Kc to 0. Jam Inputs J1, J2, J3, and J4 are used to preset the first counting section and there is no last counting section. The intermediate counting section consists of three cascaded BCD decade ( 10) counters presettable by means of Jam Inputs J5 through J16.

The Mode-Select Inputs permit frequency-synthesizer channel separations of 10, 12.5, 20, 25, or 50 parts. These inputs set the maximum value of N at 9999 (when the first counting section divides by 5 or 10) or 15,999 (when the first counting section divides by 8, 4, or 2).

The three decades of the intermediate counting section can be preset to a binary 15 instead of a binary 9, while their place values are still 1, 10, and 100, multiplied by the number of the N mode. For example in the 8 mode, the number from which counting-down begins can be preset to:

• 3rd decade: 1500
• 2nd decade: 150
• 1st decade: 15
• Last counting section 1000

The total of these numbers (2665) times 8 equals 21,320. The first counting section can be preset to 7. Therefore, 21,327 is the maximum possible count in the 8 mode.

The highest count of the various modes is shown in the column entitled Extended Counter Range of Table 1. Control inputs Kb and Kc can be used to initiate and lock the counter in the "master preset" state. In this condition the flip-flops in the counter are preset in accordance with the jam inputs and the counter remains in that state as long as Kb and Kc both remain low. The counter begins to count down from the preset state when a counting mode other than the master preset mode is selected.

The counter should always be put in the master preset mode before the 5 mode is selected.

Whenever the master preset mode is used, control signals Kb=0 and Kc=0 must be applied for at least 3 full clock pulses.

After the Master Preset Mode inputs have been changed to one of the modes, the next positive-going clock transition changes an internal flip-flop so that the countdown can begin at the second positive-going clock transition. Thus, after an MP (Master Preset) mode, there is always one extra count before the output goes high. Fig. 1 illustrates a total count of 3 ( 8 mode). If the Master Preset mode is started two clock cycles or less before an output pulse, the output pulse will appear at the time due. If the Master Preset Mode is not used the counter jumps back to the "JAM" count when the output pulse appears.

A "1" on the Latch Enable input will cause the counter output to remain high once an output pulse occurs, and to remain in the high state until the latch input returns to "0". If the Latch Enable is "0", the output pulse will remain high for only 1 cycle of the clock-input signal.

As illustrated in the sample applications, this device is particularly advantageous in communication digital frequency synthesis (VHF, UHF, FM, AM, etc.) where programmable divide-by-"N" counters are an integral part of the synthesizer phase-locked-loop sub-system. The CD4059A can also be used to perform the synthesizer "Fixed Divide-by-R" counting function. It is also useful in general-purpose counters for instrumentation functions such as totalizers, production counters, and "time out" timers.

The CD4059B-series types are supplied in 24-lead dual-in-line plastic packages (E suffix), and 24-lead small-outline packages (M and M96 suffixes).