Rainbow Electronics MAX1471 User Manual
Page 21
ing once t
CPU
has expired. At the beginning of t
RF
, the
modules selected in the power control register (register
0x0) are powered up with the exception of the peak
detectors and have the t
RF
period to settle.
At the end of t
RF
, the MAX1471 stops driving DIO low
and enables ADATA, FDATA, and peak detectors if
chosen to be active in the power configuration register
(0x0). The CPU must be awake at this point, and must
hold DIO low for the MAX1471 to remain in operation.
The CPU must begin driving DIO low any time during
t
LOW
= t
CPU
+ t
RF
. If the CPU fails to drive DIO low,
DIO is pulled high through the internal pullup resistor,
and the timer sequence is restarted, leaving the
MAX1471 powered down. Any time the DIO line is dri-
ven high while the DRX = 1, the DRX sequence is initi-
ated, as defined in Figure 12.
t
RF
is a 16-bit timer, configured through registers 0x7
(upper byte) and 0x8 (lower byte). The possible t
RF
set-
tings are in Table 12. The data written to the t
RF
register
(0x7 and 0x8) is multiplied by 120µs to give the total t
RF
time. On power-up, the RF timer registers are set to
zero and must be written before using DRX mode.
Typical Power-Up Procedure
Here is a typical power-up procedure for receiving either
ASK or FSK signals at 315MHz in continuous mode:
1) Write 0x3000 to reset the part.
2) Write 0x10FE to enable all RF and baseband sections.
3) Write 0x135F to set the oscillator frequency register
to work with a 315MHz crystal.
4) Write 0x1120 to set FSKCALLSB for an accurate
FSK calibration.
5) Write 0x1201 to begin FSK calibration.
6) Read 0x2900 and verify that bit 0 is 1 to indicate
FSK calibration is done.
The MAX1471 is now ready to receive ASK or FSK data.
Due to the high sensitivity of the receiver, it is recom-
mended that the configuration registers be changed
only when not receiving data. Receiver desensitization
may occur, especially if odd-order harmonics of the
SCLK line fall within the IF bandwidth.
MAX1471
315MHz/434MHz Low-Power, 3V/5V
ASK/FSK Superheterodyne Receiver
______________________________________________________________________________________
21
Table 6. Power Configuration Register (Address: 0x0)
BIT ID
BIT NAME
BIT LOCATION
(0 = LSB)
POWER-UP
STATE
FUNCTION
LNA_EN
LNA enable
7
0
1 = Enable LNA
0 = Disable LNA
AGC_EN
AGC enable
6
0
1 = Enable AGC
0 = Disable AGC
MIXER_EN
Mixer enable
5
0
1 = Enable mixer
0 = Disable mixer
FSKBB_EN
FSK baseband
enable
4
0
1 = Enable FSK baseband
0 = Disable FSK baseband
FSKPD_EN
FSK peak
detector enable
3
0
1 = Enable FSK peak detectors
0 = Disable FSK peak detectors
ASKBB_EN
ASK baseband
enable
2
0
1 = Enable ASK baseband
0 = Disable ASK baseband
ASKPD_EN
ASK peak
detector enable
1
0
1 = Enable ASK peak detectors
0 = Disable ASK peak detectors
SLEEP
Sleep mode
0
0
1 = Deep-sleep mode
0 = Normal operation