December 1990 2
Philips Semiconductors Product specification
Presettable synchronous 4-bit binary 
up/down counter
74HC/HCT193
FEATURES
• Synchronous reversible 4-bit binary counting
• Asynchronous parallel load
• Asynchronous reset
• Expandable without external logic
• Output capability: standard
• ICC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT193 are high-speed Si-gate CMOS devices 
and are pin compatible with low power Schottky TTL 
(LSTTL). They are specified in compliance with JEDEC 
standard no. 7A.
The 74HC/HCT193 are 4-bit synchronous binary up/down 
counters. Separate up/down clocks, CP
U
and 
CPDrespectively, simplify operation. The outputs change 
state synchronously with the LOW-to-HIGH transition of 
either clock input. If the CPUclock is pulsed while CPDis 
held HIGH, the device will count up. If the CPDclock is 
pulsed while CPUis held HIGH, the device will count down. 
Only one clock input can be held HIGH at any time, or 
erroneous operation will result. The device can be cleared 
at any time by the asynchronous master reset input (MR); 
it may also be loaded in parallel by activating the 
asynchronous parallel load input (PL).
The “193” contains four master-slave JK flip-flops with the 
necessary steering logic to provide the asynchronous 
reset, load, and synchronous count up and count down 
functions.
Each flip-flop contains JK feedback from slave to master, 
such that a LOW-to-HIGH transition on the CPDinput will 
decrease the count by one, while a similar transition on the 
CPUinput will advance the count by one.
One clock should be held HIGH while counting with the 
other, otherwise the circuit will either count by two’s or not 
at all, depending on the state of the first flip-flop, which 
cannot toggle as long as either clock input is LOW. 
Applications requiring reversible operation must make the 
reversing decision while the activating clock is HIGH to 
avoid erroneous counts.
The terminal count up (TCU) and terminal count down 
(TCD) outputs are normally HIGH. When the circuit has 
reached the maximum count state of 15, the next 
HIGH-to-LOW transition of CPUwill cause TCUto go 
LOW.
TCUwill stay LOW until CPUgoes HIGH again, duplicating 
the count up clock.
Likewise, the TCDoutput will go LOW when the circuit is in 
the zero state and the CPDgoes LOW. The terminal count 
outputs can be used as the clock input signals to the next 
higher order circuit in a multistage counter, since they 
duplicate the clock waveforms. Multistage counters will not 
be fully synchronous, since there is a slight delay time 
difference added for each stage that is added.
The counter may be preset by the asynchronous parallel 
load capability of the circuit. Information present on the 
parallel data inputs (D0to D3) is loaded into the counter 
and appears on the outputs (Q0to Q3) regardless of the 
conditions of the clock inputs when the parallel load 
(PL) input is LOW. A HIGH level on the master reset (MR) 
input will disable the parallel load gates, override both 
clock inputs and set all outputs (Q0to Q3) LOW. If one of 
the clock inputs is LOW during and after a reset or load 
operation, the next LOW-to-HIGH transition of that clock 
will be interpreted as a legitimate signal and will be 
counted.