5. Engineering Scaling and Input Attenuation: In many applications,

the input signal must be scaled, or divided down, before being applied

to the DMS-40PC. In some situations, the input signal exceeds the

full-scale range of the meter, and in other applications, a direct

one-to-one relation does not exist between the input voltage and

the desired display reading. For an example of the second situation,

assume an input voltage of 1.0Vdc is required to display a reading of

“7500” when applied to a ±2V input meter. An input divider circuit,

constructed with two series resistors with an output-to-input ratio of

0.75, will scale the 1.0V signal down to 0.75V.

Engineering scaling and input attenuation are discussed in Ap Note 4

of the DATEL Digital Panel Voltmeter Catalog. Compensating for inputs

which have a zero offset is also discussed.

6. BCD Outputs (DMS-40PC-X-RS and -RL-BCD Models Only):

Models with a “-BCD” suffix have 12 extra output pins, labeled

A through L (6 per side), that provide the following information: mul-

tiplexed serial BCD data, digit drive, and polarity indication. The data

present on pins A - L simultaneously drives the meter’s internal LED

display. All functions on pins A - L are 5V CMOS compatible, however,

they are only rated to drive one, 74LS series, TTL load. CMOS logic

IC’s, for example 74HC or 74HCT series devices, should be used when

more fan-out capability is required.

As the timing diagram in Figure 5 indicates, 100Hz is the optimum

display scan rate when the BCD outputs are used to drive external

LED displays. Faster scan rates, while permissible, are not necessary.

Slower scanning, however, may result in noticeable “flickering” of

the display. Common anode LED’s, combined with a 74LS247 BCD

to seven-segment decoder, is the simplest way of implementing an

external display. A seventy-five to one-hundred Ohm resistor on each

LS247 segment-drive output provides adequate display brightness.

The functions of pins A - L are listed below:

BCD DATA (pins I - L): Four lines are used for BCD (Binary Coded

Decimal) data outputs, representing the numbers 0 - 9. Positive-logic

convention (a high represents a “1”) is used.

DIGIT DRIVE ( pins A - E): These five outputs, when gated with STROBE,

can be used to direct the BCD DATA into external latches. DIGIT DRIVE

outputs may also be connected directly to the bases of NPN transistors

in remote-display configurations. The digits are scanned right-to-left, i.e.,

MSD (DIGIT 1 DRIVE) to LSD (DIGIT 5 DRIVE).

BUSY (pin G): This is a status pin that goes high at the start of an ana-

log-to-digital (A/D) conversion cycle and remains high until the conver-

sion ends.

STROBE (pin H): A string of five sequential, active-low, STROBE pulses

are output (after BUSY goes low) indicating the end of a conversion and

the availability of new data. The 5 STROBE pulses occur only once per

conversion, or 2.5 times each second. STROBE can be used to latch the

BCD data (on pins I - L) into external latches. Either edge can be used

since STROBE (~ 5μsec wide) is active only in the center of the cor-

responding DIGIT DRIVE and BCD DATA outputs.

POLARITY (pin F): This pin, which is also used inside the DMS-40PC to

drive the negative-sign segment, indicates whether the last input signal

conversion was positive (POLARITY set high) or negative (POLARITY set

low). POLARITY, unlike BCD DATA, is not multiplexed. For data latching

purposes, POLARITY should be sampled during the STROBE pulse for

digit 1 (most significant digit).

Figure 6. BCD Data Timing Diagram

DIGIT DRIVE 1

(MSD)

Data from

Previous Conversion

DIGIT DRIVE 2

DIGIT DRIVE 3

DIGIT DRIVE 4

DIGIT DRIVE 5

(LSD)

STROBE OUT

BCD DATA

(4 LINES)

Approx. 5μsec

5 Strobes Only Per Conversion

Approx. 2msec

Approx. 2msec

Approx. 8msec

BUSY

1

MSD

23

4

5

LSD

12

3

4

5

MPM_DMS-40PC.C03 Page 5 of 6

DMS-40PC Series

4½ Digit, LED Display Digital Panel Voltmeters

www.murata-ps.com

APPLICATIONS