MC145026

•MC145027•MC145028•SC41343•SC41344

MOTOROLA

10

RS

CTC

RTC

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 RTC CTC′

(Hz)

for 1 kHz

≤ f ≤ 400 kHz

where: CTC′ = CTC + Clayout + 12 pF

RS ≈ 2 RTC

RS ≥ 20 k

RTC ≥ 10 k

400 pF < CTC < 15 µF

The value for RS should be chosen to be ≥ 2 times RTC. This range ensures

that current through RS is insignificant compared to current through RTC. The

upper limit for RS must ensure that RS x 5 pF (input capacitance) is small com-

pared to RTC x CTC.

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 M

Ω.

Figure 10. Timing Diagram

PWmin

TE

2 WORD TRANSMISSION

ENCODER

CONTINUOUS TRANSMISSION

ENCODER

OSCILLATOR

(PIN 12)

Dout

(PIN 15)

VT

(PIN 11)

DATA OUTPUTS

1.1 (R2C2)

DECODER

ENCODING SEQUENCE

1ST

DIGIT

HIGH

2ND WORD

1ST WORD

OPEN

LOW

9TH

DIGIT

9TH

DIGIT

1ST

DIGIT