si4021 Silicon Laboratories, si4021 Datasheet - Page 27

• Manufacturer Part Number: si4021
• Description: Si4021 Universal Ism Band Fsk Transmitter
• Manufacturer: Silicon Laboratories

SIMPLIFIED INTERNAL CONTROL AND TIMING
The internal controller uses the clock generated by the crystal oscillator to sequentially process the various events and to de-bounce the
push-button (PB) inputs. If the oscillator is not running, internal logic automatically turns it on temporarily and then off again. Such events
are: any wake-up event (POR, PB press, wake-up timer timeout and low supply voltage detection), PB release and status read request by the
microcontroller.
If two wake-up events occur in succession, the crystal oscillator stays on until the next status read (acknowledgment of the first event).
Simplified Internal Control and Timing Diagrams
Push-button
Push-button
Push-button
(In terna l)
(In terna l)
(In terna l)
(inte rna l)
(inte rna l)
(inte rna l)
Osc_On
Osc_On
Osc_On
inpu t x
inpu t x
inpu t x
POR
nIRQ
POR
nIRQ
POR
Vdd
Vdd
Vdd
Microcontroller mode (ec=0, ex=0)
SP I
Microcontroller mode with multiple event read (ec=0, ex=0)
SP I
Microcontroller mode (ec=1, ex=0)
SP I
Status rd
Status rd cmd
Slee p cmd
Stat. b its
(PO R)
Tclk_tail**
Tsx*
Status rd cmd
Stat. b its
(PO R)
No te:
* Tsx : Crystal oscillator st
** Length of Tclk_tail is determined by the parameter in the Sleep comm
1us
Debouncing Time + T
Status rd cmd
Stat. b its
(PB x)
artup t im e
s x*
Status rd
Tsx*
Status rd cmd
Slee p cmd
Stat. b its
(PB x)
Tclk_tail* *
Tsx*
a nd
IA4221
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