ATA8205 datasheet(13/46 Pages) ATMEL

13 / 46 page

9121B–INDCO–04/09

ATA8203/ATA8204/ATA8205

8.2

Bit-check Mode

In bit-check mode the incoming data stream is examined to distinguish between a valid signal

from a corresponding transmitter and signals due to noise. This is done by subsequent time

frame checks where the distances between 2 signal edges are continuously compared to a pro-

grammable time window. The maximum number of these edge-to-edge tests, before the

receiver switches to receiving mode, is also programmable.

8.3

Configuring the Bit Check

Assuming a modulation scheme that contains two edges per bit, two time frame checks verify

one bit. This is valid for Manchester, Bi-phase, and most other modulation schemes. The maxi-

mum count of bits to be checked can be set to 0, 3, 6, or 9 bits using the variable N

Bit-check in the

OPMODE register. This implies 0, 6, 12, and 18 edge-to-edge checks respectively. If N

Bit-check is

set to a higher value, the receiver is less likely to switch to receiving mode due to noise. In the

presence of a valid transmitter signal, the bit check takes less time if N

Bit-check is set to a lower

value. In polling mode, the bit-check time is not dependent on NBit-check. Figure 8-2 shows an

example where three bits are tested successfully and the data signal is transferred to pin DATA.

Figure 8-2.

Timing Diagram for Complete Successful Bit Check

According to Figure 8-3, the time window for the bit check is defined by two separate time limits.

If the edge-to-edge time t

ee is in between the lower bit-check limit TLim_min and the upper

bit-check limit T

Lim_max, the check continues. If tee is smaller than TLim_min or tee exceeds TLim_max,

the bit check is terminated and the receiver switches to sleep mode.

Figure 8-3.

Valid Time Window for Bit Check

IC_ACTIVE

Data_out (DATA)

Dem_out

Bit check

Bit-check

Start-up mode

(Number of checked Bits: 3)

Bit check ok

1/2 Bit

Start-check mode

Receiving mode

Start-up

1/fSig

tee

TLim_max

TLim_min

Dem_out

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