Rainbow Electronics T5761 - Manual (Page 9)

9
T5760/T5761
4561B–RKE–10/02
• Application USA (f
XTO
= 7.14063 MHz, T
Clk
= 1.961 µs)
• Application Europe (f
XTO
= 6.77617 MHz, T
Clk
= 2.066 µs)
• Other applications The electrical characteristic is given as a function of T
Clk
.
The clock cycle of some function blocks depends on the selected baud-rate range
(BR_Range) which is defined in the OPMODE register. This clock cycle T
XClk
is defined
by the following formulas for further reference:
BR_Range = BR_Range0: T
XClk
= 8
´
T
Clk
BR_Range1: T
XClk
= 4 ´ T
Clk
BR_Range2: T
XClk
= 2
´
T
Clk
BR_Range3: T
XClk
= 1
´
T
Clk
Polling Mode
According to Figure 11, 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 low current of I
S
= I
Soff
. During the start-up period, T
Startup
,
all signal processing circuits are enabled and settled. In the following bit-check mode,
the incoming data stream is analyzed bit by bit contra a valid transmitter signal. If no
valid signal is present, the receiver is set back to sleep mode after the period T
Bit-check
.
This period varies check by check as it is a statistical process. An average value for
T
Bit-check
is given in the electrical characteristics. During T
Startup
and T
Bit-check
the current
consumption is I
S
= I
Son
. The condition of the receiver is indicated on Pin IC_ACTIVE.
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 guaran-
tee the reception of a transmitted command the transmitter must start the telegram with
an adequate preburst. The required length of the preburst depends on the polling
parameters T
Sleep
, T
Startup
, T
Bit-check
and the start-up time of a connected microcontroller
(T
Start_microcontroller
). Thus, T
Bit-check
depends on the actual bit rate and the number of bits
(N
Bit-check
) to be tested.
The following formula indicates how to calculate the preburst length.
T
Preburst
³
T
Sleep
+ T
Startup
+ T
Bit-check
+ T
Start_microcontroller
Sleep Mode The length of period T
Sleep
is defined by the 5-bit word Sleep of the OPMODE register,
the extension factor XSleep (according to Table 8), and the basic clock cycle T
Clk
. It is
calculated to be:
T
Sleep
= Sleep ´ X
Sleep
´ 1024 ´ T
Clk
In US- and European applications, the maximum value of T
Sleep
is about 60 ms if XSleep
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 XSleep to 8. XSleep can be set to 8 by bit
XSleep
Std
to’1’.
According to Table 7, the highest register value of sleep sets the receiver into a perma-
nent 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 and may also be used for microcontroller polling – via
Pin POLLING/_ON, the receiver can be switched on and off.
I
Spoll
I
Soff
T
Sleep
I
Son
T
Startup
T
Bit-check
+ ( ) ´ + ´
T
Sleep
T
Startup
T
Bit-check
+ +
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