C8051T620/1/6/7 & C8051T320/1/2/3
132
Rev. 1.2
21.4. Clock Multiplier
The C8051T620/1/6/7 & C8051T320/1/2/3 device includes a 48 MHz high-frequency oscillator instead of a
12 MHz oscillator and a 4x Clock Multiplier, so the USB0 module can be run directly from the internal high-
frequency oscillator. For compatibility with the Flash development platform, however, the CLKMUL register
(SFR Definition 21.4) behaves as if the Clock Multiplier is present.
SFR Address = 0xB9
SFR Definition 21.4. CLKMUL: Clock Multiplier Control
Bit
7
6
5
4
3
2
1
0
Name
MULEN
MULINIT
MULRDY
MULSEL[1:0]
Type
R
R
R
R
R
R
R
Reset
1
1
1
0
0
0
0
0
Bit
Name
Description
Write
Read
7
MULEN
Clock Multiplier Enable Bit.
0: Clock Multiplier disabled.
1: Clock Multiplier enabled.
This bit always reads 1.
6
MULINIT
Clock Multiplier Initialize
Bit.
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.
This bit always reads 1.
5
MULRDY
Clock Multiplier Ready Bit.
0: Clock Multiplier not ready.
1: Clock Multiplier ready (locked).
This bit always reads 1.
4:2
Unused
Read = 000b; Write = Don’t Care
1:0
MULSEL[1:0]
Clock Multiplier Input Select Bits.
These bits select the clock supplied to the Clock Multiplier.
00: Internal High-Frequency Oscillator
01: External Oscillator
10: External Oscillator/2
11: Reserved.
These bits always read 00.