C8051F320-TB Silicon Laboratories Inc, C8051F320-TB Datasheet - Page 122

• Manufacturer Part Number: C8051F320-TB
• Description: BOARD PROTOTYPING W/C8051F320
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F320-TB

• Contents: Board
• Processor To Be Evaluated: C8051F320/F321
• Interface Type: USB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F320
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

C8051F320/1
13.3. 4x Clock Multiplier
The 4x Clock Multiplier allows a 12 MHz oscillator to generate the 48 MHz clock required for Full Speed
USB communication (see Section “15.4. USB Clock Configuration” on page 146). A divided version of the
Multiplier output can also be used as the system clock. See Section 13.4 for details on system clock and
USB clock source selection.
The 4x Clock Multiplier is configured via the CLKMUL register. The procedure for configuring and enabling
the 4x Clock Multiplier is as follows:
Important Note: When using an external oscillator as the input to the 4x Clock Multiplier, the exter-
nal source must be enabled and stable before the Multiplier is initialized. See Section 13.4 for
details on selecting an external oscillator source.
122
Bit7:
Bit6:
Bit5:
Bits4–2: Unused. Read = 000b; Write = don’t care.
Bits1–0: MULSEL: Clock Multiplier Input Select
MULEN
R/W
Bit7
1. Reset the Multiplier by writing 0x00 to register CLKMUL.
2. Select the Multiplier input source via the MULSEL bits.
3. Enable the Multiplier with the MULEN bit (CLKMUL | = 0x80).
4. Delay for >5 µs.
5. Initialize the Multiplier with the MULINIT bit (CLKMUL | = 0xC0).
6. Poll for MULRDY => ‘1’.
MULEN: Clock Multiplier Enable
0: Clock Multiplier disabled.
1: Clock Multiplier enabled.
MULINIT: Clock Multiplier Initialize
This bit should be a ‘0’ when the Clock Multiplier is enabled. Once enabled, writing a ‘1’ to
this bit will initialize the Clock Multiplier. The MULRDY bit reads ‘1’ when the Clock Multiplier
is stabilized.
MULRDY: Clock Multiplier Ready
This read-only bit indicates the status of the Clock Multiplier.
0: Clock Multiplier not ready.
1: Clock Multiplier ready (locked).
These bits select the clock supplied to the Clock Multiplier.
MULINIT MULRDY
R/W
Bit6
SFR Definition 13.4. CLKMUL: Clock Multiplier Control
MULSEL
00
01
10
11
Bit5
R
R/W
Bit4
-
External Oscillator / 2
External Oscillator
Internal Oscillator
Selected Clock
RESERVED
Rev. 1.4
R/W
Bit3
-
R/W
Bit2
-
R/W
Bit1
MULSEL
R/W
Bit0
SFR Address
00000000
Reset Value
0xB9