11
4899B–RKE–10/06
ATA3741
5.2
Polling Mode
As shown in
, the receiver stays in polling mode in a continuous cycle of
three different modes. In sleep mode, the signal processing circuitry is disabled for the time
period T
Sleep
while consuming a low current of I
S
= I
Soff
. During the start-up period, T
Startup
, all sig-
nal processing circuits are enabled and settled. In the following bit-check mode, the incoming
data stream is analyzed bit by bit against a valid transmitter signal. If no valid signal is present,
the receiver is set back to sleep mode after the period T
Bitcheck
. This period varies check by
check as it is a statistical process. An average value for T
Bitcheck
is given in
. During T
Startup
and T
Bitcheck
the current consumption is I
S
= I
Son
. The average
current consumption in polling mode is dependent on the duty cycle of the active mode and can
be calculated as:
During T
Sleep
and T
Startup
, the receiver is not sensitive to a transmitter signal. To guarantee the
reception of a transmitted command, the transmitter must start the telegram with an adequate
preburst. The required length of the preburst is dependent on the polling parameters T
Sleep
, T
Star-
tup
, T
Bitcheck
, and the startup time of a connected microcontroller (T
Start_µC
). T
Bitcheck
thus depends
on the actual bit rate and the number of bits (N
Bitcheck
) to be tested.
The following formula indicates how to calculate the preburst length.
T
Preburst
≥
T
Sleep
+ T
Startup
+ T
Bitcheck
+ T
Start_
µ
C
5.2.1
Sleep Mode
The length of period T
Sleep
is defined by the 5-bit word Sleep of the OPMODE register, on the
extension factor X
Sleep
, and on the basic clock cycle T
Clk
. It is
calculated to be:
In US and European applications, the maximum value of T
Sleep
is about 60 ms if X
Sleep
is set to 1.
The time resolution is about 2 ms in that case. The sleep time can be extended to almost half a
second by setting X
Sleep
to 8. X
Sleep
can be set to 8 by bit X
SleepStd
or by bit X
SleepTemp
, resulting in
a different mode of action as described below:
X
SleepStd
= 1 implies the standard extension factor. The sleep time is always extended.
X
SleepTemp
= 1 implies the temporary extension factor. The extended sleep time is used as long
as every bit check is OK. If the bit check fails once, this bit is set back to 0 automatically, result-
ing in a regular sleep time. This functionality can be used to save current in the presence of a
modulated disturber similar to an expected transmitter signal. The connected microcontroller is
rarely activated in that condition. If the disturber disappears, the receiver switches back to regu-
lar polling and is again sensitive to appropriate transmitter signals.
As seen in
, the highest register value of Sleep sets the receiver to a per-
manent sleep condition. The receiver remains in that condition until another value for Sleep is
programmed into the OPMODE register. This function is desirable where several devices share
a single data line.
I
Spoll
I
Soff
T
Sleep
I
Son
T
Startup
T
Bitcheck
+
(
)
×
+
×
T
Sleep
T
Startup
T
Bitcheck
+
+
------------------------------------------------------------------------------------------------------------
=
T
Sleep
Sleep
X
Sleep
×
1024
×
T
Clk
×
=
