AN95089 Datasheet, PDF (7/19 Pages) Ramtron International Corporation – BLE Crystal Oscillator Selection and Tuning Techniques

PSoC® 4/PRoC™ BLE Crystal Oscillator Selection and Tuning Techniques
4.1 Steps to Correct Clock Inaccuracy
Step 1: Enable radio
Step 2: Enable WCO
Step 3: Enable ECO
Step 4: Bring the ECO clock on a GPIO and observe the clock accuracy (Example - clock on Port 2 Pin 7)
Step 5: Trim the internal capacitance to achieve 0 ppm
Function Code:
void trim_capacitance()
{
/* Step1:Enable Radio */
*(uint32*) CYREG_BLE_BLESS_RF_CONFIG = 0x01;
/* Step2:Enable WCO */
*(uint32*) CYREG_BLE_BLESS_WCO_CONFIG |= 0x80000000;
/* Step3:Enable ECO */
*(uint32*) CYREG_BLE_BLERD_DBUS = 0xC992;
/* Step4:Configure pin 2[7] as ECO crystal Output */
*(uint32*) CYREG_GPIO_PRT2_PC = 0xDB6DB6;
*(uint32*) CYREG_HSIOM_PORT_SEL2 |= 0xA0000000;
/* Step5:Trim Load Capacitance */
*(uint32*) CYREG_BLE_BLERD_BB_XO_CAPTRIM = <Load Cap value >;
}
Details for these registers are available in PSoC 4/PRoC BLE Registers Technical Reference Manuals (TRMs):
PSoC 4 BLE registers TRM and PRoC BLE registers TRM
The load capacitance value in step 5 is a 16-bit hex value. Each bit adds 0.1011 pF capacitance.
Bits 15-8 together control the capacitance at the XI node.
Bits 14 – 8 are used for fine control of the capacitance value at the XI node.
Decimal Value of Bits 14-8
0
1
2
Capacitance Value C1
3.6900 pF
3.7911 pF
3.8922 pF
…….
……..
127
16.428 pF
Bit 15 is used for coarse control of the capacitance value at the XI node.
Bit 15 = 0 means that no additional capacitance is turned ON at the XI node.
Bit 15 = 1 means that an additional capacitance of 8.1 pF is turned ON at the XI node.
Bits 7-0 together control the capacitance at the XO node.
Bits 6-0 are used for fine control of the capacitance value at the XO node.
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Document No. 001-95089 Rev. *A
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