SM8211M Datasheet, PDF (8/22 Pages) Nippon Precision Circuits Inc – POCSAG Decoder For Pagers

SM8211M
Operating Modes
The SM8211M has four operating modes—Switch-
ON, Preamble, Idle and Lock modes. Note that all
values in parentheses in the following figures are for
the case when the speed is 1200 bps.
Switch-ON mode
After power is applied and after RST has gone LOW
to reset all internal circuits, code words for the 27-bit
flag data and the six 18-bit addresses are received
from the CPU on TX-DATA and are stored. As each
code word comprises 32 bits, this process takes (32 ×
7) + 1 TX-CLK cycles to complete. When the 225
TX-CLK cycles have been received, BS1, BS2 and
BS3 are set and device operation transfers to pream-
ble mode.
RST
1 to 200 ms
X
TX-CLK
1
2
224
225
TX-DATA
127 ms (54.2 ms)
BS1
BS2
(BS2 flag = 0)
1.953 x N ms
(0.833 x N ms)
BS2
(BS2 flag = 1)
BS3
1.953 x M ms
(0.833 x M ms)
Preamble mode
X > 2 ms for external system clock operation or during continuous oscillations
X > 900 ms for internal oscillator operation immediately after power is applied or BACKUP is released (V_DD = 1.5 to 3.5 V)
X > 1.5 s for internal oscillator operation immediately after power is applied or BACKUP is released (V_DD < 1.5 V)
Figure 3. Switch-ON mode timing
NIPPON PRECISION CIRCUITS—8