CD4541B

CD4541B programmable timer consists of a 16-stage binary counter, an oscillator that is controlled by external R-C compo- nents (2 resistors and a capacitor), an automatic power-on reset circuit, and output control logic. The counter increments on positive-edge clock transitions and can also be reset via the MASTER RESET input.

The output from this timer is the Q or Q output from the 8th, 10th, 13th, or 16th counter stage. The desired stage is chosen using time-select inputs A and B (see Frequency Select Table). The output is available in either of two modes selectable via the MODE input, pin 10 (see Truth Table).When this MODE input is
a logic "1", the CD4541B output will be a continuous square wave having a frequency equal to the oscillator frequency divided by 2N. With the CD4541B MODE input set to logic "0" and after a MASTER RESET is initiated, the output (assuming Q output has been selected) changes from a low to a high state after 2N-1 counts
and remains in that state until another MASTER RESET pulse is applied or the MODE input is set to a logic "1".

CD4541B Timing is initialized by setting the AUTO RESET input (pin 5) to logic "0" and turning power on. If pin 5 is set to logic "1", the AUTO RESET circuit is disabled and counting will not start until after a positive MASTER RESET pulse is applied and returns to a low level. The AUTO RESET consumes an appreciable amount of power and should not be used if low-power operation is desired. For reliable automatic power-on reset, VDD should be greater than 5V.

The CD4541B RC oscillator, shown in Figure 2, oscillates with a frequency determined by the RC network and is calculated using: