SM8212 datasheet(19/32 Pages) NPC

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NIPPON PRECISION CIRCUITS-19

SM8212B

8. Miscellaneous Interface Pins

(1) SIGNAL

(2) XT, XTN

(3) CLKO

(4) RSTN

(5) AREA

Crystal oscillator element connection pins.

The SM8212B operates at 76.8 kHz system clock speed,

and this clock can be provided simply by connecting a crys-

tal element between XT and XTN. The oscillator amplifi-

er, feedback resistance and oscillator capacitance are all

built-in.

In this case, XTN should not be used as a clock to drive

an external device. Also, a 1000 pF to 0.1 µF capacitor

should be connected between XVSS and VDD.

Clock output pin. The clock output can be used as a

CPU sleep clock or melody IC (SM1124 series) clock.

The output clock frequency, 76.8 or 38.4 kHz, is selected

using the decoder parameter set command.

Decoder IC internal initialization reset pin. It also func-

tions as an oscillator start-up booster (current source)

immediately after power is applied to speed up oscillator

stabilization.

This pin goes HIGH for

≥ 1 second when a sync code is

detected with 2 or less random bit errors in preamble, lock

or idle mode sync code detection timing.

During intermittent-duty CPU operation, monitoring

this pin is useful for out-of-range signal strength.

However, even if a sync code is detected, this pin is not

held HIGH for

≥ 1 second if 2 consecutive sync codes

could not be detected, or under the following situations in

1200 and 2400 bps modes.

When the second of 2 consecutive sync codes could

not be detected but a 6-bit preamble is detected and

preamble continues.

When operation transfers from lock mode to idle

mode and then to preamble mode. Note that if opera-

tion stays in idle mode after transfer from lock mode,

this pin goes HIGH for

≥ 1 second.

NRZ-format signal input pin, with built-in noise can-

celler filter.

Current pager systems operate at 3 baud rates (512, 1200

and 2400 bps). In conventional systems, the RF stage LPF

time constants are changed in response to the baud rate in

order to get the best possible reception. However, this

requires changing the external components which results in

increased product operating costs.

The SM8212B, however, performs digital processing on

the input signal which allows the 3 baud rates to be cov-

ered without the need to substitute RF stage LPF compo-

nents. The side effect of this digital filter processing is a

small probability of rate errors occurring.

Digital processing can be turned ON/OFF using flags.

When turned ON, there are 4 filter constant settings that

can be selected to obtain the best possible reception condi-

tions in a flexible manner (see “Parameter Flags” section).

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