Rev. 1.2
129
C8051T620/1/6/7 & C8051T320/1/2/3
SFR Address = 0xA9
SFR Definition 21.1. CLKSEL: Clock Select
Bit
7
6
5
4
3
2
1
0
Name
USBCLK[2:0]
OUTCLK
CLKSL[2:0]
Type
R
R/W
R/W
R/W
Reset
0
0
0
0
0
0
0
0
Bit
Name
Function
7
Unused
Read = 0b; Write = Don’t Care
6:4
USBCLK[2:0]
USB Clock Source Select Bits.
000: USBCLK derived from the Internal High-Frequency Oscillator.
001: USBCLK derived from the Internal High-Frequency Oscillator / 8.
010: USBCLK derived from the External Oscillator.
011: USBCLK derived from the External Oscillator / 2.
100: USBCLK derived from the External Oscillator / 3.
101: USBCLK derived from the External Oscillator / 4.
110: USBCLK derived from the Internal Low-Frequency Oscillator.
111: RESERVED.
3
OUTCLK
Crossbar Clock Out Select.
If the SYSCLK signal is enabled on the Crossbar, this bit selects between outputting
SYSCLK and SYSCLK synchronized with the Port I/O pins.
0: Enabling the Crossbar SYSCLK signal outputs SYSCLK.
1: Enabling the Crossbar SYSCLK signal outputs SYSCLK synchronized with the
Port I/O.
2:0
CLKSL[2:0]
System Clock Source Select Bits.
000: SYSCLK derived from the Internal High-Frequency Oscillator and scaled per
the IFCN bits in register OSCICN.
001: SYSCLK derived from the External Oscillator circuit.
010: SYSCLK derived from the Internal High-Frequency Oscillator / 2.
011: SYSCLK derived from the Internal High-Frequency Oscillator.
100: SYSCLK derived from the Internal Low-Frequency Oscillator and scaled per
the OSCLD bits in register OSCLCN.
101-111: RESERVED.