Rainbow Electronics ATmega128RFA1 - Manual (Page 118)

118
8266A-MCU Wireless-12/09
ATmega128RFA1
Bit 3 2 1 0
NA ($152) XTAL_TRIM3 XTAL_TRIM2 XTAL_TRIM1 XTAL_TRIM0 XOSC_CTRL
Read/Write RW RW RW RW
Initial Value 0 0 0 0
This register controls the operation of the 16MHz crystal oscillator.
• Bit 7:4 – XTAL_MODE3:0 - Crystal Oscillator Operating Mode
These register bits set the operating mode of the 16 MHz crystal oscillator. For normal
operation the default value is set to XTAL_MODE = 0xF after reset. For use with an
external clock source it is recommended to set XTAL_MODE = 0x4.
Table 9-58 XTAL_MODE Register Bits
Register Bits Value Description
0x4 Internal crystal oscillator disabled; use
external reference frequency. XTAL_MODE3:0
0xF Internal crystal oscillator enabled; amplitude
regulation of oscillation enabled.
• Bit 3:0 – XTAL_TRIM3:0 - Crystal Oscillator Load Capacitance Trimming
These register bits control two internal capacitance arrays connected to pins XTAL1
and XTAL2. A capacitance value in the range from 0 pF to 4.5 pF is selectable with a
resolution of 0.3 pF.
Table 9-59 XTAL_TRIM Register Bits
Register Bits Value Description
0x0 0.0 pF, trimming capacitors disconnected
0x1 0.3 pF, trimming capacitor switched on
0x2 ...
XTAL_TRIM3:0
0xF 4.5 pF, trimming capacitor switched on
9.12.23 RX_SYN – Transceiver Receiver Sensitivity Control Register
Bit 7 6
NA ($155) RX_PDT_DIS Res2 RX_SYN
Read/Write RW R
Initial Value 0 0
Bit 5 4
NA ($155) Res1 Res0 RX_SYN
Read/Write R R
Initial Value 0 0
Bit 3 2
NA ($155) RX_PDT_LEVEL3 RX_PDT_LEVEL2 RX_SYN
Read/Write RW RW
Initial Value 0 0
Bit 1 0
NA ($155) RX_PDT_LEVEL1 RX_PDT_LEVEL0 RX_SYN
Read/Write RW RW
Initial Value 0 0