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TC835CBU

PERSONAL COMPUTER DATA ACQUISITION A/D CONVERTER

TelCom Semiconductor Inc => Microchip 

PERSONAL COMPUTER

DATA ACQUISITION A/D CONVERTER

1

TC835

V+

REF

IN

TC835

ANALOG

COMMON

V+

6.8V

ZENER

IZ

V–

V+

V+

6.8 kΩ

REF

IN

TC835

TC04

20

k Ω 1.25V REF

ANALOG

COMMON

ANALOG

GROUND

Figure 5. Using an External Reference

Digital Section Functional Description

The major digital subsystems within the TC835 are

illustrated in Figure 6, with timing relationships shown in

Figure 7. The multiplexed BCD output data can be displayed

on LCD or LED display with the TC7211A (LCD)

4-digit display driver.

The digital section is best described through a discus-

sion of the control signals and data outputs.

RUN/HOLD Input (Pin 25)

When left open, this pin assumes a logic "1" level. With

a R/H = 1, the TC835 performs conversions continuously,

with a new measurement cycle beginning every 40,002

clock pulses.

When R/H changes to a logic "0," the measurement

cycle in progress will be completed, and data held and

displayed as long as the logic "0" condition exists.

A positive pulse (>300nsec) at R/H initiates a new

measurement cycle. The measurement cycle in progress

when R/H initially assumed the logic "0" state must be

completed before the positive pulse can be recognized as a

single conversion run command.

TELCOM SEMICONDUCTOR, INC.

POLARITY D5

MSB

FROM

ANALOG

SECTION

POLARITY

FF

LATCH

D4

DIGIT

D3

D2

D1

DRIVE

SIGNAL

MULTIPLEXER

LSB

DATA

OUTPUT

13 B1

14 B2

15 B4

16 B8

LATCH

LATCH

LATCH

LATCH

2

ZERO

CROSS

DETECT

COUNTERS

24

22

DIGITAL CLOCK

GND

IN

25

RUN/

HOLD

CONTROL LOGIC

27

OVER–

RANGE

28

UNDER–

RANGE

26

STROBE

21

BUSY

3

Figure 6. Digital Section Functional Diagram

INTEGRATOR

OUTPUT

SIGNAL

SYSTEM INTE

ZERO 10,000

10,001 COUNTS

COUNTS (FIXED)

REFERENCE

INTEGRATE

20,001

COUNTS (MAX)

FULL MEASUREMENT CYCLE

40,002 COUNTS

BUSY

 ,
 OVERRANGE

WHEN

APPLICABLE

UNDERRANGE

,WHEN

4

5

APPLICABLE

EXPANDED SCALE

BELOW

DIGIT SCAN

D5

D4

D3

D2

6

100

COUNTS

STROBE

DIGIT SCAN

FOR

OVERRANGE

AUTO ZERO

* D5

D4

D1

* FIRST D5 OF SYSTEM ZERO

AND REFERENCE INTEGRATE

ONE COUNT LONGER.

SIGNAL

INTEGRATE

REFERENCE

INTEGRATE

*

7

D3

D2

D1

Figure 7. Timing Diagrams for Outputs

8

3-71

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