74LS中文资料安森美半导体数据手册PDF规格书

SYNCHRONOUS 4-BIT UP/DOWN COUNTER

The SN54 /74LS669 is a synchronous 4-bit up/down counter. The LS669 is a 4-bit binary counter. For high speed counting applications, this presettable counter features an internal carry lookahead for cascading purposes. By clocking all flip-flops simultaneously so the outputs change coincident with each other (when instructed to do so by the count enable inputs and internal gating) synchronous operation is provided. This helps to eliminate output counting spikes, normally associated with asynchronous (ripple-clock) count ers. The four master-slave flip-flops are triggered on the rising (positive-going) edge of the clock waveform by a buffered clock input.

• Programmable Look-Ahead Up/Down Binary/Decade Counters

• Fully Synchronous Operation for Counting and Programming

• Internal Look-Ahead for Fast Counting

• Carry Output for n-Bit Cascading

• Fully Independent Clock Circuit

• Buffered Outputs