5

FN3159.3

September 15, 2015

Detailed Description

DECODE Operation

For the lCM7218A/B products, there are 3 input data formats

possible; either direct segment and decimal point information (8

bits per digit) or two Binary formats plus decimal point

information (Hexadecimal/Code B formats with 5 bits per digit).

The 7-segment decoder on chip is disabled when direct

segment information is to be written. In this format, the

inputs directly control the outputs as follows:

Here, "Ones" represent "on" segments for all inputs except

the Decimal Point. For the Decimal Point "zero" represents

an "on" segment.

HEXAdecimal/CODE B Decoding

For all products, a choice of either HEXA or Code B decoding

may be made. HEXA decoding provides 7-segment numeric

plus six alpha characters while Code B provides a negative

sign (-), a blank (for leading zero blanking), certain useful

alpha characters and all numeric formats.

The four bit binary code is set up on inputs lD3-lD0, and

decimal point data is set up on ID7.

SHUTDOWN

SHUTDOWN performs several functions: it puts the device

into a very low dissipation mode (typically 10

turns off both the digit and segment drivers, and stops the

multiplex scan oscillator (this is the only way the scan

oscillator can be disabled). However, it is still possible to input

data to the memory during shutdown - only the display output

sections of the device are disabled in this mode.

Powerdown

In the Shutdown Mode, the supply voltage may be reduced to

2V without data in memory being lost. However, data should

not be written into memory if the supply voltage is less than 4V.

Output Drive

The common anode output drive is approximately 200mA per

digit at a 12% duty cycle. With segment peak drive current of

40mA typically, this results in 5mA average drive. The common

cathode drive capability is approximately one-half that of the

common anode drive. If high impedance LED displays are

used, the drive current will be correspondingly less.

FIGURE 2. MULTIPLEX TIMING (COMMON CATHODE VERSION)

Input Data:

ID7

lD6

ID5 lD4 lD3 lD2 lD1 ID0

Output Segments:

D.P.

ab

c

e

g

f

d

FIGURE 3. SEGMENT ASSIGNMENTS

DECIMAL 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

15

HEXA

CODE

0 123 4 5 6 7 8 9 A B C D E

F

CODE B

0 1 2 3 4 5 6 7 8 9 -

E H L P (BLANK)

ICM7218