C8051F987-GMR Silicon Labs, C8051F987-GMR Datasheet - Page 203

• Manufacturer Part Number: C8051F987-GMR
• Description: 8-bit Microcontrollers - MCU 8kB 512B RAM
• Manufacturer: Silicon Labs

Specifications of C8051F987-GMR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

20.2.4. 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.
LOADCAP
0000
0001
0010
0100
0101
1000
1001
1010
0011
0110
0111
1011
1100
1101
1110
1111
Table 20.2. SmaRTClock Load Capacitance Settings
Crystal Load Capacitance
10.5 pF
12.5 pF
13.5 pF
11.5 pF
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
Rev. 1.1
C8051F99x-C8051F98x
Equivalent Capacitance seen on
XTAL3 and XTAL4
10.0 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
23.0 pF
25.0 pF
27.0 pF
11.0 pF
21.0 pF
9.0 pF
8.0 pF
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