مدار مجتمع (آی سی) آی سی‌کاربرد ویژه

Product Attributes

Introduction

These synchronous, presettable counters feature internal carry lookahead for high-speed counting designs. The S160 and S162 are 4-bit decade counters, while the S161 and S163 are 4-bit binary counters. The carry output is decoded through a NOR gate to prevent glitches during normal counting operation. Synchronous operation is achieved by clocking all flip-flops simultaneously, causing the outputs to change together under the direction of the count enable inputs and internal gating. This mode of operation eliminates the output count glitches typically associated with asynchronous (ripple clock) counters. The buffered clock input triggers all four flip-flops on the rising (positive) edge of the clock input waveform. These counters are fully programmable — that is, the outputs can be preset to any level. Since presetting is synchronous, setting the load input low disables the counter and causes the outputs to agree with the setup data after the next clock pulse, regardless of the levels of the enable inputs. The carry lookahead circuit enables cascading of counters for n-bit synchronous applications without additional gating; the key to this feature is the two count enable inputs and one ripple carry output. Both count enable inputs (P and T) must be high to count, and input T is fed forward to enable the ripple carry output. The enabled ripple carry output produces a high-level output pulse with a duration approximately equal to the high portion of the QA output. This high-level overflow ripple carry pulse can be used to enable successive cascaded stages.

Features

• Synchronous programmable
• Internal look-ahead for fast counting
• Carry output for n-bit cascading
• Synchronous counting
• Load control line
• Diode-clamped inputs
• Typical propagation time, clock to Q output: 9 ns
• Typical clock frequency: 70 MHz
• Typical power dissipation: 475 mW

Applications

• High-speed counter design
• Synchronous counting applications
• n-bit cascading applications