SM8213 datasheet(9/33 Pages) NPC

9 / 33 page

SM8213AM

NIPPON PRECISION CIRCUITS—9

Idle signal

In the POCSAG format, for pager systems that send

numeric data, the message information content var-

ies and as a result an idle signal or another address

signal is inserted after the message to indicate the

end of the message.

That is, if no address word or message word exists

for a frame within a batch or for a code word within

a frame, the idle pattern, shown in table 3, is trans-

mitted in its place. Then during message signal

reception, the message ends when the idle signal is

detected.

The SM8213AM supports 2 methods of determining

the end of message. Namely, a message ends when

either an idle signal or another address is received

(POCSAG format), or when an interrupt signal from

the CPU is received.

Receive signal duty factor

During preamble detection, the preamble pattern

(1,0) is recognized at duty factors from 25% (min) to

75% (max) of the (1,0) preamble cycle.

Error correction and detection

The SM8213AM performs error correction (or

detection) on each code word as described in table 4.

Note that there are 8 selectable error correction con-

ditions for the preamble pattern.

An error is deemed to have occurred when 2 or more

signal edges occur within 1-bit unit time, and a rate

error is deemed to have occurred when the number of

errors exceeds the counter value. Refer to the “Pre-

amble Mode” section for a discussion of the error

counter.

Table 3. Idle code format

Bit number

Bit value

Bit number

Bit value

Bit number

Bit value

Bit number

Bit value

1091

100181260

110190270

120200281

131210290

140220301

150230311

161241321

Table 4. Error correction

Item

Description

Preamble Pattern Detection

Selectable 1 to 8 rate errors in 6 to 544 bits

Synchronization Code word

Detection 2 random errors in 32 bits

Self Address Code word

Detection 2 random errors in 32 bits

Message Code word

1-bit and 2-bit burst errors in 31 bits

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