1. General description
The 74HC161 is a synchronous presettable binary counter with an internal look-head carry.
Synchronous operation is provided by having all flip-flops clocked simultaneously on the positivegoing
edge of the clock (CP). The outputs (Q0 to Q3) of the counters may be preset HIGH or LOW.
A LOW at the parallel enable input (PE) disables the counting action and causes the data at the
data inputs (D0 to D3) to be loaded into the counter on the positive-going edge of the clock. Preset
takes place regardless of the levels at count enable inputs (CEP and CET). A LOW at the master
reset input (MR) sets Q0 to Q3 LOW regardless of the levels at input pins CP, PE, CET and CEP
(thus providing an asynchronous clear function). The look-ahead carry simplifies serial cascading
of the counters. Both CEP and CET must be HIGH to count. The CET input is fed forward to enable
the terminal count output (TC). The TC output thus enabled will produce a HIGH output pulse of a
duration approximately equal to a HIGH output of Q0. This pulse can be used to enable the next
cascaded stage. The maximum clock frequency for the cascaded counters is determined by the CP
to TC propagation delay and CEP to CP set-up time, according to the following formula:
Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to
voltages in excess of VCC.
2. Features and benefits
• Wide supply voltage range from 2.0 V to 6.0 V
• CMOS low power dissipation
• High noise immunity
• Latch-up performance exceeds 100 mA per JESD 78 Class II Level B
• Complies with JEDEC standards:
• JESD8C (2.7 V to 3.6 V)
• JESD7A (2.0 V to 6.0 V)
• CMOS input levels
• Synchronous counting and loading
• 2 count enable inputs for n-bit cascading
• Asynchronous reset
• Positive-edge triggered clock
• ESD protection:
• HBM JESD22-A114F exceeds 2000 V
• MM JESD22-A115-A exceeds 200 V
• Specified from -40 °C to +85 °C and -40 °C to +125 °C