BC352239A Datasheet, PDF (97/116 Pages) List of Unclassifed Manufacturers – BlueCore 3-Multimedia External

Device Terminal Descriptions
8.11 TCXO Enable OR Function
An OR function exists for clock enable signals from a host controller and BlueCore3-Multimedia External where
either device can turn on the clock without having to wake up the other device. PIO[3] can be used as the Host
clock enables input and PIO[2] can be used as the OR output with the TCXO enable signal from
BlueCore3-Multimedia External.
VDD
TCXO
GSM System
Enable
CLK IN
CLK REQ OUT
BlueCore System
CLK REQ IN/
PIO[3]
CLK REQ OUT/
XTAL IN
PIO[2]
Figure 8.34: Example TXCO Enable OR Function
On reset and up to the time the PIO has been configured, PIO[2] will be tri-stated. Therefore, the developer must
ensure that the circuitry connected to this pin is pulled via a 470kΩ resistor to the appropriate power rail. This
ensures that the TCXO is oscillating at start up.
8.12 RESET and RESETB
BlueCore3-Multimedia External may be reset from several sources: RESET or RESETB pins, power on reset, a
UART break character or via a software configured watchdog timer.
The RESET pin is an active high reset and is internally filtered using the internal low frequency clock oscillator. A
reset will be performed between 1.5 and 4.0ms following RESET being active. It is recommended that RESET be
applied for a period greater than 5ms. The RESETB pin is the active low version of RESET and is ‘ORed’ on chip
with the active high RESET with either causing the reset function.
The power on reset occurs when the VDD_CORE supply falls below typically 1.5V and is released when
VDD_CORE rises above typically 1.6V.
At reset the digital I/O pins are set to inputs for bi-directional pins and outputs are tristated. The PIOs have weak
pull-downs.
Following a reset, BlueCore3-Multimedia External assumes the maximum XTAL_IN frequency, which ensures
that the internal clocks run at a safe (low) frequency until BlueCore-Multimedia is configured for the actual
XTAL_IN frequency. If no clock is present at XTAL_IN, the oscillator in BlueCore3-Multimedia External free runs,
again at a safe frequency.
BC352239A-ds-001Pc
© Cambridge Silicon Radio Limited 2004
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