MRF24J40_08 Datasheet, PDF (118/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.15.1.2 Sleep Clock Calibration
The SLPCLK frequency is calibrated by a 20-bit
SLPCAL register clocked by the 20 MHz main oscillator
(50 ns period). Sixteen samples of the SLPCLK are
counted and stored in the SLPCAL register. To perform
SLPCLK calibration:
1. Select the source of SLPCLK.
2. Begin calibration by setting the SLPCALEN bit
(SLPCAL2 0x20B<4>) to ‘1’. Sixteen samples of
the SLPCLK are counted and stored in the
SLPCAL register.
3. Calibration is complete when the SLPCALRDY
bit (SLPCAL2 0x20B<7>) is set to ‘1’.
The 20-bit SLPCAL value is contained in registers,
SLPCAL2, SLPCAL1 and SLPCAL0 (0x20B<3:0>,
0x20A and 0x209). The Sleep clock period is calculated
as follows:
P_SLPCAL = SLPCAL * 50 ns/16
The SLPCLK frequency can be slowed by setting the
Sleep Clock Division (SLPCLKDIV) bits (SLPCON1
0x220<4:0>).
3.15.1.3 Sleep Mode Counters
Figure 3-16 shows the Sleep mode counters. A
summary of the counters are:
Main Counter (0x229<1:0>, 0x228, 0x227, 0x226) – A
26-bit counter clocked by SLPCLK. Together with the
Remain Counter times events as listed in Table 3-19.
Remain Counter (0x225, 0x224) – A 16-bit counter
clocked by MAINCLK. Together with the Main Counter
times events as listed in Table 3-19.
Wake Time (0x223<2:0>, 0x222) – An 11-bit value that
is compared with the main counter value to signal the
time to enable (wake-up) the 20 MHz main oscillator.
Table 3-20 gives the recommended values for
WAKETIME depending on the SLPCLK frequency.
Wake Count (0x36<4:3>, 0x35<6:0>) – A 9-bit counter
clocked by SLPCLK. During the time the wake counter
is counting, the 20 MHz main oscillator is starting up,
stabilizing and disabled to the RF, baseband and MAC
circuitry. The recommended wake count period is 2 ms
to allow the 20 MHz main oscillator to stabilize.
Table 3-20 gives the recommended values for
WAKECNT depending on the SLPCLK frequency.
TABLE 3-19: MAIN AND REMAIN COUNTER
TIMED EVENTS
Mode
Timed Event
Beacon-Enabled
Coordinator
Beacon-Enabled Device
Nonbeacon-Enabled
Coordinator or Device
Beacon Interval (BI)
Inactive Period
Sleep Interval
TABLE 3-20: WAKE TIME AND WAKE
COUNT RECOMMENDED
VALUES
SLPCLK
Source
SLPCLKDIV
WAKETIME
(2.1 ms)
WAKECNT
(2 ms)
100 kHz
32 kHz
0x01
0x00
0x0D2
0x045
0x0C8
0x042
DS39776B-page 116
Preliminary
© 2008 Microchip Technology Inc.