74HC191 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2017. All rights reserved.
Product data sheet Rev. 3 — 3 January 2017 4 of 22
NXP Semiconductors
74HC191
Presettable synchronous 4-bit binary up/down counter
6. Functional description
[1] H = HIGH voltage level
L = LOW voltage level
l = LOW voltage level one set-up time prior to the LOW-to-HIGH clock transition
X = don’t care
= LOW-to-HIGH clock transition
[1] H = HIGH voltage level
L = LOW voltage level
X = don’t care
= one LOW level pulse
= TC goes LOW on a LOW-to-HIGH clock transition
Table 3. Function table
[1]
Operating mode Input Output
PL U/D CE CP Dn Qn
parallel load L X X X L L
LXXXHH
count up H L l X count up
count down H H l X count down
Hold (do nothing) H X H X X no change
Table 4. TC and RC Function table
[1]
Input Terminal count state Output
U/D CE CP Q0 Q1 Q2 Q3 TC RC
H HXHHHHLH
L HXHHHHHH
L L HHHH
L HXLLLLLH
H HXLLLLHH
H L LLLL
