sm8211m Nippon Precision Circuits Inc, (NPC), sm8211m Datasheet - Page 9

• Manufacturer Part Number: sm8211m
• Description: Pocsag Decoder For Pagers
• Manufacturer: Nippon Precision Circuits Inc, (NPC)

Preamble mode
Preamble mode is a continuous 544-bit long period.
If neither a preamble pattern, rate error nor sync code
is detected during this period, operation transfers to
idle mode.
If a preamble pattern is detected, the preamble mode
544-bit long period is recommenced.
If a rate error is detected, device operation transfers
to idle mode. (A single error occurs when two active
edges occur in the received signal on SIG-IN within
1-bit unit time. A rate error occurs when the number
of errors in the error counter equals the error thresh-
old set by flags ER0 to ER2. The error counter is
reset when a preamble pattern is detected.)
If the sync code is detected, SYN-VAL goes HIGH
and operation transfers to lock mode. (If an error of 2
bits or less occurs, the detected word is recognized as
the sync code.)
(BS2 flag = 0)
(BS2 flag = 1)
BS1
BS2
BS2
BS3
(0.833 x N ms)
1.953 x N ms
Preamble count starts
Preamble signal
Figure 5. Preamble pattern sequence
Receive timing
(0.833 x M ms)
1.953 x M ms
(26.7 ms)
62.5 ms
Figure 4. Idle mode timing
... 1 0 1 0 1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 ...
Counting
Count reset to 0
SM8211M
Error bit
X
Idle mode
In idle mode, a check is made for the presence of a
preamble signal when the RF intermittent-duty con-
trol signals (BS1, BS2, BS3) for battery saving are
active. If a preamble pattern is detected, operation
immediately transfers to preamble mode. If a pream-
ble pattern is not detected, intermittent-duty opera-
tion continues.
A preamble pattern is detected when either a 101010
or 010101 6-bit pattern is detected. Since there is a
reasonable probability that this simple pattern can
occur during a valid communicated signal (data, not
preamble), this 6-bit pattern makes returning to pre-
amble mode easier. This is useful for cases where
weak electric fields, noise or other temporary inter-
ference cause device operation to transfer to idle
mode. Further, if a sync code is detected within one
cycle after device operation has transferred from
lock mode, device operation returns to lock mode. (If
flag BS2 is 0, pin BS2 does not go HIGH during the
cycle after device operation has transferred from
lock mode.)
Preamble count restarts
1062.5 ms (453.3 ms)
Preamble detected
NIPPON PRECISION CIRCUITS—9