Rainbow Electronics MAX1471 User Manual
Page 17
Discontinuous Receive Mode (DRX = 1)
In the discontinuous receive mode (DRX = 1), the
power signals of the different modules of the MAX1471
toggle between OFF and ON, according to internal
timers t
OFF
, t
CPU
, and t
RF
. It is also necessary to write
the frequency divisor of the external crystal in the oscil-
lator frequency register (register 0x3). This number is
the integer result of f
XTAL
/ 100kHz. Before entering the
discontinuous receive mode for the first time, it is also
necessary to calibrate the timers (see the Calibration
section).
The MAX1471 uses a series of internal timers (t
OFF
,
t
CPU
, and t
RF
) to control its power-up. The timer
sequence begins when both CS and DIO are one. The
MAX1471 has an internal pullup on the DIO pin, so the
user must tri-state the DIO line when CS goes high.
The external CPU can then go to a sleep mode during
t
OFF
. A high-to-low transition on DIO, or a low level on
DIO serves as the wake-up signal for the CPU, which
must then start its wake-up procedure, and drive DIO
low before t
LOW
expires (t
CPU
+ t
RF
). Once t
RF
expires,
the MAX1471 enables the FSKOUT and/or ASKOUT
data outputs. The CPU must then keep DIO low for as
long as it may need to analyze any received data.
Releasing DIO causes the MAX1471 to pull up DIO,
reinitiating the t
OFF
timer.
Oscillator Frequency Register (Address: 0x3)
The MAX1471 has an internal frequency divider that
divides down the crystal frequency to 100kHz. The
MAX1471 uses the 100kHz clock signal when calibrating
itself and also to set the image-rejection frequency. The
hexadecimal value written to the oscillator frequency reg-
ister is the nearest integer result of f
XTAL
/ 100kHz.
MAX1471
315MHz/434MHz Low-Power, 3V/5V
ASK/FSK Superheterodyne Receiver
______________________________________________________________________________________
17
Figure 9. Data Input Diagram
SCLK
A2
A1
D0
ADDRESS
DATA
DIO
C3
A3
C0
C1
C2
A0
D7
D6
D5
D4
D3
D2
D1
COMMAND
CS
Figure 10. Read Command on a 4-Wire SERIAL Interface
SCLK
CS
0
0
1
0
0
0
0
0
0
0
0
0
A3
A2
A1
A0
DIO
C3
C2
C1
C0
A3
A2
A1
A0
D0
D7
COMMAND
ADDRESS
DATA
READ
COMMAND
ADDRESS
DATA
ADATA (IF DOUT_ASK = 1)
R7
R6
R5
R4
R3
R2
R1
R0
R0
R7
REGISTER DATA
REGISTER
DATA
FDATA (IF DOUT_FSK = 1)
R7
R6
R5
R4
R3
R2
R1
R0
R0
R7
REGISTER DATA
REGISTER
DATA