MM516
User's Manual
41
Revision 1.4 7-8-2011
Hardware Description Manual
5.7 TCXO Enable OR Function
An OR function exists for clock enable signals from a host controller and BlueCore 5 chip 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 BlueCore 5 chip.
Figure 23
Example of OR Function
On reset and up to the time the PIO has been configured, PIO[2] will be tristate. Ensure that the circuitry connected
to this pin is pulled via a 470k resistor to the appropriate power rail. This ensures that the TCXO is oscillating at start
up.
5.8 Reset
BlueCore 5 chip may be reset from several sources: RESETB pin, power on reset, a UART break character or
via a software configured watchdog timer.
The RESETB pin is an active low reset and is internally filtered using the internal low frequency clock oscillator. A
reset will be performed between 1.5 and 4.0ms following RESETB being active. It is recommended that RESETB
be applied for a period greater than 5ms.
The power on reset occurs when the VDD_CORE supply falls below typically 1.26V and is released when VDD_CORE
rises above typically 1.31V. At reset the digital I/O pins are set to inputs for bidirectional pins and outputs are tristate.
The PIOs have weak pull-downs. Following a reset, BlueCore 5 chip assumes the maximum XTAL_IN frequency,
which ensures that the internal clocks run at a safe (low) frequency until BlueCore 5 chip is configured for the
actual XTAL_IN frequency. If no clock is present at XTAL_IN, the oscillator in BlueCore 5 chip free runs, again
at a safe frequency.
