7217(1997) Ver la hoja de datos (PDF) - Intersil

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componentes Descripción

Fabricante

7217
(Rev.:1997)

4-Digit LED Display, Programmable Up/Down Counter

Intersil 

ICM7217

Detailed Description

Control Outputs

Display Outputs and Control

The CARRY/BORROW output is a positive going pulse

occurring typically 500ns after the positive going edge of the

COUNT INPUT. It occurs when the counter is clocked from

9999 to 0000 when counting up and from 0000 to 9999 when

counting down. This output allows direct cascading of

counters. The CARRY/BORROW output is not valid during

load counter and reset operation. When the count is 6000 or

higher, a reset generates a CARRY/BORROW pulse.

The EQUAL output assumes a negative level when the

contents of the counter and register are equal.

The ZERO output assumes a negative level when the

content of the counter is 0000.

The CARRY/BORROW, EQUAL and ZERO outputs will drive

a single TTL load over the full range of supply voltage and

ambient temperature; for a logic zero, these outputs will sink

1.6mA at 0.4V and for a logic one, the outputs will source

>60µA. A 10kΩ pull-up resistor to VDD on the EQUAL or

ZERO outputs is recommended for highest speed operation,

and on the CARRY/BORROW output when it is being used

for cascading. Figure 2 shows control outputs timing

diagram.

The Digit and SEGment drivers provide a decoded

7-segment display system, capable of directly driving com-

mon anode LED displays at typical peak currents of

35mA/seg. This corresponds to average currents of

8mA/seg at 25% multiplex duty cycle. For the common cath-

ode versions, peak segment currents are 12.5mA, corre-

sponding to average segment currents of 3.1mA. Figure 1

shows the multiplex timing. The DISPLAY pin controls the

display output using three level logic. The pin is self-biased

to a voltage approximately 1/2 (VDD); this corresponds to

normal operation. When this pin is connected to VDD, the

segments are disabled and when connected to VSS, the

leading zero blanking feature is inhibited. For normal opera-

tion (display on with leading zero blanking) the pin should be

left open. The display may be controlled with a 3 position

SPDT switch; see Test Circuit.

Multiplex SCAN Oscillator

The on-board multiplex scan oscillator has a nominal free-

running frequency of 2.5kHz. This may be reduced by the

addition of a single capacitor between the SCAN pin and the

positive supply. Capacitor values and corresponding nominal

oscillator frequencies, digit repetition rates, and loading

times are shown in Table 1.

R1

10kΩ

1MΩ

R2

20kΩ

SCAN INPUT

ICM7217

C

0.01µF

FIGURE 10A.

1MΩ

500Ω

500Ω

SCAN INPUT

ICM7217

0.01µF

FIGURE 10B.

VDD = 5V

10kΩ

78

4

3kΩ

200Ω

0.05µF

ICM7555

3

2

61

8s

0.05µF

SCAN INPUT

ICM7217

0V

FIGURE 10C.

FIGURE 10. BRIGHTNESS CONTROL CIRCUITS

9-18

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