Functional Description

7-segment displays with minimal interface with the display

and the data source. Serial data transfer from the data

source to the display driver is accomplished with 2 signals,

serial data and clock. Since the MM5452 does not contain a

character generator, the formatting of the segment informa-

tion must be done prior to inputting the data to the MM5452.

Using a format of a leading “1” followed by the 32 data bits

allows data transfer without an additional load signal. The 32

data bits are latched after the 36th clock is complete, thus

providing non-multiplexed, direct drive to the display. Out-

puts change only if the serial data bits differ from the previ-

ous time.

A block diagram is shown in

Figure 1. For the MM5452 a

DATA ENABLE is used instead of the 33rd output. If the

DATA ENABLE signal is not required, the 33rd output can be

brought out. This is the MM5453 device.

Figure 5 shows the input data format. A start bit of logical “1”

precedes the 32 bits of data. At the 36th clock a LOAD signal

is generated synchronously with the high state of the clock,

which loads the 32 bits of the shift registers into the latches.

At the low state of the clock a RESET signal is generated

which clears all the shift registers for the next set of data.

The shift registers are static master-slave configuration.

There is no clear for the master portion of the first shift

register, thus allowing continuous operation.

If the clock is not continuous, there must be a complete set

of 36 clocks otherwise the shift registers will not clear.

Figure 2 shows the pin-out of the MM5452. Bit 1 is the first

bit following the start bit and it will appear on pin 18.

Figure 4 shows the timing relationships between data, clock

and DATA ENABLE.

Figure 6 shows a typical application. Note how the input data

maps to the output pins and the display. The MM5452 and

MM5453 do not have format restrictions, as all outputs are

controllable. The application assumes a specific display

pinout. Different display/driver connection patterns will, of

course, yield a different input data format.

00613704

FIGURE 4.

00613705

FIGURE 5. Input Data Format

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