MC145026•MC145027•MC145028•SC41343•SC41344 MOTOROLA
10
R
S
C
TC
R
TC
11 12 13
INTERNAL
ENABLE
Figure 9. Encoder Oscillator Information
This oscillator operates at a frequency determined by the
external RC network; i.e.,
f ≈
1
2.3 R
TC
C
TC
′
(Hz)
for 1 kHz ≤ f ≤ 400 kHz
where: C
TC
′ = C
TC
+ C
layout
+ 12 pF
R
S
≈ 2 R
TC
R
S
≥ 20 k
R
TC
≥ 10 k
400 pF < C
TC
< 15 µF
The value for R
S
should be chosen to be ≥ 2 times R
TC
. This range ensures
that current through R
S
is insignificant compared to current through R
TC
. The
upper limit for R
S
must ensure that R
S
x 5 pF (input capacitance) is small com-
pared to R
TC
x C
TC
.
For frequencies outside the indicated range, the formula is less accurate.
The minimum recommended oscillation frequency of this circuit is 1 kHz. Sus-
ceptibility to externally induced noise signals may occur for frequencies below
1 kHz and/or when resistors utilized are greater than 1 MΩ.
Figure 10. Timing Diagram
PW
min
TE
2 WORD TRANSMISSION
ENCODER
CONTINUOUS TRANSMISSION
ENCODER
OSCILLATOR
(PIN 12)
D
out
(PIN 15)
VT
(PIN 11)
DATA OUTPUTS
1.1 (R
2
C
2
)
DECODER
ENCODING SEQUENCE
1ST
DIGIT
HIGH
2ND WORD1ST WORD
OPEN LOW
9TH
DIGIT
9TH
DIGIT
1ST
DIGIT
2
4
6
16
18
20
22
24
26
28
30
80
82
84
86
88
90
114
116
118
120
122
178
180
182
184
