TC7135CBU datasheet(10/24 Pages) MICROCHIP

10 / 24 page

TC7135

DS21460C-page 10

 2004 Microchip Technology Inc.

FIGURE 5-2:

Timing Diagrams For

Outputs.

5.1

RUN/HOLD Input

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

a RUN/HOLD = 1, the TC7135 performs conversions

continuously, with a new measurement cycle beginning

every 40,002 clock pulses.

When RUN/HOLD changes to a logic ‘0’, the measure-

ment cycle in progress will be completed, with the data

held and displayed as long as the logic ‘0’ condition

exists.

A positive pulse (>300 nsec) at RUN/HOLD initiates a

new measurement cycle. The measurement cycle in

progress when RUN/HOLD initially assumed the logic

‘0’ state must be completed before the positive pulse

can be recognized as a single conversion run

command.

The new measurement cycle begins with a 10,001

count auto-zero phase. At the end of this phase, the

busy signal goes high.

5.2

STROBE Output

During the measurement cycle, the STROBE control

line is pulsed low five times. The five low pulses occur

in the center of the digit drive signals (D1, D2, D3, D5)

(see Figure 5-3).

D5 (MSD) goes high for 201 counts when the

measurement cycles end. In the center of the D5 pulse,

101 clock pulses after the end of the measurement

cycle, the first STROBE occurs for one half clock pulse.

After the D5 digit strobe, D4 goes high for 200 clock

pulses. The STROBE then goes low 100 clock pulses

after D4 goes high. This continues through the D1 digit

drive pulse.

The digit drive signals will continue to permit display

scanning. STROBE pulses are not repeated until a new

measurement is completed. The digit drive signals will

not continue if the previous signal resulted in an

overrange condition.

The active-low STROBE pulses aid BCD data transfer

to UARTs, processors and external latches. For more

information, please refer to Application Note 784

(DS00784).

FIGURE 5-3:

Strobe Signal Low Five

Times Per Conversion.

Integrator

Output

Overrange when

Applicable

Underrange when

Applicable

System

Zero

10,001

Counts

Signal

Integrate

10,000

Counts

(Fixed)

Reference

Integrate

20,001

Counts (Max)

Full Measurement Cycle

40,002 Counts

Busy

Expanded Scale Below

100

Counts

Digit Scan

STROBE

Auto-Zero

Signal

Integrate

Reference

Integrate

Digit Scan

for Overrange

* First D5 of System Zero and

Reference Integrate One Count

Longer

End of Conversion

(MSD)

Data

Busy

B1 B8

STROBE

Data

(LSD)

Data

Note Absence

of STROBE

201

Counts

200

Counts

200

Counts

200

Counts

200

Counts

200

Counts

200

Counts

*Delay between Busy going Low and First STROBE pulse is

dependent on Analog Input.

TC835

Outputs

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