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RFM22 Datasheet(PDF) 58 Page - HOPE Microelectronics CO., Ltd. |
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RFM22 Datasheet(HTML) 58 Page - HOPE Microelectronics CO., Ltd. |
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58 / 150 page  R F M 2 2 Tel: +86-755-82973805 Fax: +86-755-82973550 E-mail: sales@hoperf.com http://www.hoperf.com 58 8.6. Wake-Up Timer The RFM22 contains an integrated wake-up timer which periodically wakes the module from SLEEP mode. Thewake-up timer runs from the internal 32.768 kHz RC Oscillator. The wake-up timer can be configured to run when in SLEEP mode. If enwt = 1 in "Register 07h. Operating Mode and Function Control 1" when entering SLEEP mode, the wake-up timer will count for a time specified by the Wake-Up Timer Period in Registers 10h –12h. At the expiration of this period an interrupt will be generated on the nIRQ pin if this interrupt is enabled. The microcontroller will then need to verify the interrupt by reading the Interrupt Status Registers 03h –04h. The wake-up timer value may be read at any time by the wtv[15:0] read only registers 13h –14h. The formula for calculating the Wake-Up Period is the following: WUT = 32 X M X 2R-D 32.768 ms WUT Register Description wtr[3:0] R Value in Formula wtr[1:0] D Value in Formula wtm[15:0] M Value in Formula Use of the D variable in the formula is only necessary if finer resolution is required than the R value gives. Ad R/W Function/Descri ption D7 D6 D5 D4 D3 D2 D1 D0 POR Def. 14 R/W Wake-Up Timer Period 1 wtr[3] wtr[2] wtr[1] wtr[0] wtd[1] wtd[0] 00h 15 R/W Wake-Up Timer Period 2 wtm [15] wtm[14] wtm[13] wtm[12] wtm[11] wtm[10] wtm[9] wtm[8] 00h 16 R/W Wake-Up Timer Period 3 wtm [7] wtm[6] wtm[5] wtm[4] wtm[3] wtm[2] wtm[1] wtm[0] 00h 17 R Wake-Up Timer Value 1 wtv[ 15] wtv[14] wtv[13] wtv[12] wtv[11] wtv[10] wtv[9] wtv[8] — 18 R Wake-Up Timer Value 2 wtv[ 7] wtv[6] wtv[5] wtv[4] wtv[3] wtv[2] wtv[1] wtv[0] — There are two different methods for utilizing the wake-up timer (WUT) depending on if the WUT interrupt is enabled in ―Register 06h. Interrupt Enable 2,‖. If the WUT interrupt is enabled then nIRQ pin will go low when the timer expires. The module will also change state so that the 30 M XTAL is enabled so that the microcontroller clock output is available for the microcontroller to use process the interrupt. The other method of use is to not enable the WUT interrupt and use the WUT GPIO setting. In this mode of operation the module will not change state until commanded by the microcontroller. The two different modes of operation of the WUT are demonstrated in Figure 28. A 32 kHz XTAL may also be used for better timing accuracy. By setting the x32 ksel bit in 07h, GPIO0 is automatically reconfigured so that an external 32 kHz XTAL may be connected to this pin. In this mode, the GPIO0 is extremely sensitive to parasitic capacitance, so only the XTAL should be connected to this pin and the XTAL should be physically located as close to the pin as possible. Once the x32 ksel bit is set, all internal functions such as WUT, micro-controller clock, and LDC mode will use the 32 K XTAL and not the 32 kHz RC oscillator. |
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