4-bit binary counters 74F161A, 74F163A
FEATURES
• Synchronous counting and loading
• Two count enable inputs for n-bit cascading
• Positive edge-triggered clock
• Asynchronous Master Reset (74F161A)
• Synchronous Reset (74F163A)
• High speed synchronous expansion
• Typical count rate of 130MHz
• Industrial range (–40°C to +85°C) available
DESCRIPTION
4-bit binary counters feature an internal carry look-ahead and can be
used for high-speed counting. Synchronous operation is provided by
having all flip-flops clocked simultaneously on the positive-going
edge of the clock. The clock input is buffered.
The outputs of the counters may be preset to High or Low level. A
Low level at the Parallel Enable (PE) input disables the counting
action and causes the data at the D0–D3 inputs to be loaded into
the counter on the positive-going edge of the clock (provided that
the setup and hold requirements for PE are met). Preset takes place
regardless of the levels at Count Enable (CEP, CET) inputs.
A Low level at the Master Reset (MR) input sets all the four outputs
of the flip-flops (Q0 – Q3) in 74F161A to Low levels, regardless of
the levels at CP, PE, CET and CEP inputs (thus providing an
asynchronous clear function). For the 74F163A, the clear function is
synchronous. A Low level at the Synchronous Reset (SR) input sets
all four outputs of the flip-flops (Q0 – Q3) to Low levels after the next
positive-going transition on the clock (CP) input (provided that the
setup and hold time requirements for SR are met). This action
occurs regardless of the levels at PE, CET, and CEP inputs. The
synchronous reset feature enables the designer to modify the
maximum count with only one external NAND gate (see Figure 1).
The carry look-ahead simplifies serial cascading of the counters.
Both Count Enable (CEP and CET) inputs must be High to count.
The CET input is fed forward to enable the TC output. The TC
output thus enabled will produce a High output pulse of a duration
approximately equal to the High level output of Q0. This pulse can
be used to enable the next cascaded stage (see Figure 2). The TC
output is subjected to decoding spikes due to internal race
conditions. Therefore, it is not recommended for use as clock or
asynchronous reset for flip-flops, registers, or counters.
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