CD4541BC_02 Datasheet, PDF (2/8 Pages) Fairchild Semiconductor – Programmable Timer

Truth Table
Pin
State
0
1
5 Auto Reset Operating Auto Reset Disabled
6 Timer Operational
Master Reset On
9 Output Initially Low
Output Initially High
after Reset
after Reset
10 Single Cycle Mode
Recycle Mode
Division Ratio Table
Number of
A
B
Counter Stages
n
0
0
13
0
1
10
1
0
8
1
1
16
Count
2ⁿ
8192
1024
256
65536
Operating Characteristics
With Auto Reset pin set to a “0” the counter circuit is initial-
ized by turning on power. Or with power already on, the
counter circuit is reset when the Master Reset pin is set to
a “1”. Both types of reset will result in synchronously reset-
ting all counter stages independent of counter state.
The RC oscillator frequency is determined by the external
RC network, i.e.:
and R_S ≈ 2 R_tc where R_S ≥ 10 kΩ
The time select inputs (A and B) provide a two-bit address
to output any one of four counter stages (2⁸, 2¹⁰, 2¹³, and
2¹⁶). The 2ⁿ counts as shown in the Division Ratio Table
represent the Q output of the Nth stage of the counter.
When A is “1”, 2¹⁶ is selected for both states of B.
However, when B is “0”, normal counting is interrupted and
the 9th counter stage receives its clock directly from the
oscillator (i.e., effectively outputting 2⁸).
The Q/Q select output control pin provides for a choice of
output level. When the counter is in a reset condition and
Q/Q select pin is set to a “0” the Q output is a “0”. Corre-
spondingly, when Q/Q select pin is set to a “1” the Q output
is a “1”.
When the mode control pin is set to a “1”, the selected
count is continually transmitted to the output. But, with
mode pin “0” and after a reset condition the RS flip-flop
resets (see Logic Diagram), counting commences and after
2^n−1 counts the RS flip-flop sets which causes the output to
change state. Hence, after another 2^n−1 counts the output
will not change. Thus, a Master Reset pulse must be
applied or a change in the mode pin level is required to
reset the single cycle operation.
Typical RC Oscillator
Characteristics
RC Oscillator Frequency as a
Function of R_TC and C
Solid Line = R_TC = 56 kΩ, R_S = 1 kΩ and C = 1000 pF
f = 10.2 kHz @ V_DD = 10V and T_A = 25°
Dashed Line = R_TC = 56 kΩ, R_S = 120 kΩ and C = 1000 pF
f = 7.75 kHz @ V_DD = 10V and T_A = 25°
Line A: f as a function of C and (R_TC = 56 kΩ; R_S = 120k
Line B: f as a function of R_TC and (C = 100 pF; R_S = 2 R_TC
www.fairchildsemi.com
2