si4430 Silicon Laboratories, si4430 Datasheet - Page 61

• Manufacturer Part Number: si4430
• Description: Si4430 Ism Transceiver
• Manufacturer: Silicon Laboratories

8.6. Wake-Up Timer
The chip contains an integrated wake-up timer which periodically wakes the chip from SLEEP mode. The wake-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 14h–16h. 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 17h–18h.
The formula for calculating the Wake-Up Period is the following:
Use of the D variable in the formula is only necessary if finer resolution is required than the R value gives.
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,” on page 84. If the WUT interrupt is enabled then nIRQ pin will go low when
the timer expires. The chip 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 chip 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.
Add R/W Function/Description
14
15
16
17
18
R/W
R/W
R/W
R
R
Wake-Up Timer Period 1
Wake-Up Timer Period 2 wtm[15] wtm[14] wtm[13] wtm[12] wtm[11] wtm[10] wtm[9] wtm[8]
Wake-Up Timer Period 3
Wake-Up Timer Value 1
Wake-Up Timer Value 2
wtv[15] wtv[14] wtv[13] wtv[12] wtv[11]
wtm[7]
WUT Register
wtv[7]
D7
wtm[15:0]
wtr[4:0]
WUT
wtm[6]
wtv[6]
Preliminary Rev. 0.4
D6

32
wtm[5]
wtv[5]
32

M Value in Formula
D5
R Value in Formula
M
.
768
Description

2
wtm[4]
wtv[4]
wtr[4]
R
D4
ms
wtm[3]
wtv[3]
wtr[3]
D3
wtv[10]
wtm[2]
wtv[2]
wtr[2]
D2
wtm[1] wtm[0]
wtv[9]
wtv[1]
wtr[1]
D1
wtv[8]
wtv[0]
wtr[0]
Si4430
D0
POR Def.
03h
00h
00h
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