C8051F93X Datasheet, PDF (207/330 Pages) Silicon Laboratories – Pipelined intstruction architecture executes 70 of instruction in 1 or 2 system clocks

C8051F93x-C8051F92x
20.2.3. Programmable Load Capacitance
The programmable load capacitance has 16 values to support crystal oscillators with a wide range of rec-
ommended load capacitance. If Automatic Load Capacitance Stepping is enabled, the crystal load capaci-
tors start at the smallest setting to allow a fast startup time, then slowly increase the capacitance until the
final programmed value is reached. The final programmed loading capacitor value is specified using the
LOADCAP bits in the RTC0XCF register. The LOADCAP setting specifies the amount of on-chip load
capacitance and does not include any stray PCB capacitance. Once the final programmed loading capaci-
tor value is reached, the LOADRDY flag will be set by hardware to logic 1.
When using the SmaRTClock oscillator in Self-Oscillate mode, the programmable load capacitance can be
used to fine tune the oscillation frequency. In most cases, increasing the load capacitor value will result in
a decrease in oscillation frequency. Table 20.2 shows the crystal load capacitance for various settings of
LOADCAP.
Table 20.2. SmaRTClock Load Capacitance Settings
LOADCAP
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Crystal Load Capacitance
4.0 pF
4.5 pF
5.0 pF
5.5 pF
6.0 pF
6.5 pF
7.0 pF
7.5 pF
8.0 pF
8.5 pF
9.0 pF
9.5 pF
10.5 pF
11.5 pF
12.5 pF
13.5 pF
Equivalent Capacitance seen on
XTAL3 and XTAL4
8.0 pF
9.0 pF
10.0 pF
11.0 pF
12.0 pF
13.0 pF
14.0 pF
15.0 pF
16.0 pF
17.0 pF
18.0 pF
19.0 pF
21.0 pF
23.0 pF
25.0 pF
27.0 pF
Rev. 1.3
207