During normal discharge the phone indicates the user that the battery will drain after some time. If not recharged, SW detects that battery voltage is too low and shuts the phone off through a normal power down procedure.
Anyway, if the SW fails to power down the phone, CCONT will make a reset and power down the phone if the battery voltage drops below 2.8 V.
If the MAD receives fault indication, from the line TXF, that the transmitter is on although it shouldn't be, the control SW will power down the phone.
The phone can enter SLEEP only when both MCU and DSP request it. A substantial amount of current is saved in SLEEP. When going to SLEEP following things will happen
1. Both MCU and DSP enable sleep mode, set the sleep timer and enter sleep mode
2. RFCEN and RFCSETTLED -> 0 -> COBBACLK will stop (gated in COBBA). Also VR1 is disabled -> VCXO supply voltage is cut off -> RFC stops.
3. LCD display remains the same, no changes
4. Sleep clock (SLCLK) and watchdog in CCONT running
5. Sleep counter in MAD running, uses SLCLK
In the typical case phone leaves the SLEEP-mode when the SLEEP-counter in MAD expires. After that MAD enables VR1 ^ VCXO starts running ^ after a pre-programmed delay RFCSETTLED rises => MAD receives COBBACLK clock ^ MAD operation re-starts.
There are also many other cases when the SLEEP mode can be interrupted, in these cases MAD enables the VR1 and operation is started similarly
- some MCU or DSP timer expires
- DSP regular event interrupt happens
- MBUS activity is detected
- FBUS activity is detected
- Charger is connected, Charger interrupt to MAD
- any key on keyboard is pressed, interrupt to MAD
- HEADSETINT, from system connector XMIC line (EAD)
- HOOKINT, from system connector XEAR line
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