MRF24J40_08 Datasheet, PDF (117/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.15 Sleep
The MRF24J40 can be placed into a low-current Sleep
mode. During Sleep, the 20 MHz main oscillator is turned
off, disabling the RF, baseband and MAC circuitry. Data
is retained in the control and FIFO registers and the
MRF24J40 is accessible via the SPI port. There are two
Sleep modes:
• Timed Sleep Mode
• Immediate Sleep and Wake Mode
3.15.1 TIMED SLEEP MODE
The Timed Sleep Mode uses several counters to time
events for the Sleep and wake-up of the MRF24J40.
The following sections cover Sleep clock generation,
calibration and counters.
FIGURE 3-15:
SLEEP CLOCK GENERATION
3.15.1.1 Sleep Clock Generation
Figure 3-15 shows the Sleep clock generation circuitry.
The Sleep Clock (SLPCLK) frequency is selectable
between a 100 kHz internal oscillator or a 32 kHz
external crystal oscillator. The Sleep Clock Enable
(SLPCLKEN) bit in the SLPCON0 (0x211<0>) register
can enable (SLPCLKEN = 0; default setting) or disable
(SLPCLKEN = 1) the Sleep clock oscillators. The
SLPCLK frequency can be further divided by the Sleep
Clock Divisor (SLPCLKDIV) 0x220<4:0> bits. The
SLPCLK frequency can be calibrated; the procedure is
listed in Section 3.15.1.2 “Sleep Clock Calibration”
below.
SLPCALEN
SLPCALRDY
(SLPCAL2 0x20B<4>) (SLPCAL2 0x20B<7>)
LPOSC2
LPOSC1
32 kHz
External Oscillator
EN
01
100 kHz
10
Internal Oscillator
EN
MAINCLK
Sleep Calibration Counter
(SLPCAL<19:0>)
Count 16 SLPCLK Periods
Sleep Clock Divisor
(SLPCLKDIV<4:0>)
SLPCLK
SLPCLKEN
(SLPCON0 0x211<0>)
SLPCLKSEL
(RFCON7 0x207<7:6>)
The 100 kHz internal oscillator requires no external
components. However, it is not as accurate or stable as
the 32 kHz external crystal oscillator. It is recom-
mended that it be calibrated before use. See
Section 3.15.1.2 “Sleep Clock Calibration” below for
the Sleep clock calibration procedure.
To select the 100 kHz internal oscillator as the source
of SLPCLK, set the SLPCLKSEL bits (RFCON7
0x207<7:6> to ‘10’)
The 32 kHz external crystal oscillator provides better
frequency accuracy and stability than the 100 kHz
internal oscillator. The 32 kHz external crystal oscillator
external circuitry is explained in detail in Section 2.7
“32 kHz External Crystal Oscillator”.
To select the 32 kHz external crystal oscillator as the
source of SLPCLK, set the SLPCLKSEL bits (RFCON7
0x207<7:6>) to ‘01’.
© 2008 Microchip Technology Inc.
Preliminary
DS39776B-page 115