74HC390; 74HCT390

应用领域

The 74HC390; 74HCT390 is a dual 4-bit decade ripple counter divided into four separately clocked sections. The counters have two divide-by-2 sections and two divide-by-5 sections. These sections share an asynchronous master reset input (nMR) and can be used in a BCD decade or bi-quinary configuration. If master reset inputs (1MR and 2MR) are used to simultaneously clear all 8 bits of the counter, a number of counting configurations are possible within one package. The separate clocks (nCP0 and nCP1) of each section allow ripple counter or frequency division applications of divide-by-2, 4, 5, 10, 20, 25, 50 or 100. Each section is triggered by the HIGH-to-LOW transition of the clock inputs (nCP0 and nCP1). For BCD decade operation, the nQ0 output is connected to the nCP1 input of the divide-by-5 section. For bi-quinary decade operation, the nQ3 output is connected to the nCP0 input and nQ0 becomes the decade output. A HIGH on the nMR input overrides the clocks and sets the four outputs