The on-chip crystal oscillator circuit works with an offchip crystal to generate a high precision clock. It has an accuracy of 100 ppm (0.01%) and is capable of providing system clocks for Fusion peripherals and other the system clock networks, both on-chip and off. When combined with the on-chip CCC/PLL blocks, a wide range of clock frequencies can be created to support various design requirements.
The Real Time Counter inside the Analog Block has the following features:
The MATCH signal on the output of the system asserts when the value in the counter matches the value specified in the match register. Also, there is an optional output RTCPSMMATCH that is triggered on match. The RTCPSMMATCH signal must be connected to the RTCPSM macro such the Voltage Regulator activates when the Match signal is asserted.
If you use the RTC, RTCCLK must be driven by the External Crystal Oscillator driving the Fusion device and the mode of the Crystal oscillator must be controlled by the RTC.
The figure below shows the Real Time Counter dialog box.
Real Time Counter Dialog Box
Crystal Oscillator Mode
RC network - Oscillator is configured to work with an external resistor-capacitor network.
LOW_GAIN / MEDIUM_GAIN / HIGH_GAIN - Oscillator is configured to support an external crystal or ceramic resonator. The difference is the supported crystal frequency or resonator, as shown in the table below.
|
Mode |
Recommended Capacitor |
Frequency Range (in MHz) |
|
LOW_GAIN |
100 pf |
0.032 to 0.20 |
|
MEDIUM_GAIN |
100 pf |
0.21 to 2.0 |
|
HIGH_GAIN |
15 pf |
2.1 to 20.0 |
Match Register Value
The MATCH signal asserts when it is equal to this value; this is a 40 bit binary or a 10 bit hex value.
Counter Initial Value
You may specify a different counter start value. The default is zero. This also is a 40 binary or a 10 bit hex value.
On Match - Defines the actions to perform when a match occurs. You can:
Reset counter - Resets the counter once the match occurs. This can be disabled for an application that measures elapsed time.
Enable Voltage Regulator - Asserts the RTCPSMMATCH to activate the Voltage Regulator
Enable dynamic update of matchregister and counter - This option provides access to the ACM Address and Data signals to update the values of counter and match register. Exercise caution: The ACM address bus is shared by the Analog System and the Analog system configuration could be overwritten if it accesses an incorrect address.