Usb interface clock, Registers – Rainbow Electronics AT89C5122 User Manual
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AT8xC5122/23
4202E–SCR–06/06
USB Interface Clock
The USB Interface uses two clocks :
–
The first one is the CPU clock used for the interface with the microcontroller,
CK_IDLE.
–
The second one is the CK_USB supplied from the PLL through a divider by
2.
Registers
Reset Value = XXXX XXX0b
Reset Value = XXXX 1111b
Table 24. Clock Selection Register - CKSEL (S:85h)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
CKS
Bit Number Bit Mnemonic Description
7:1
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
0
CKS
CPU Oscillator Select Bit
Set this bit to connect CPU and Peripherals to PLL output.
Clear this to to connect CPU and Peripherals to XTAL1 clock input.
Table 25. Clock Reload Register - CKRL (S:97h)
7
6
5
4
3
2
1
0
-
-
-
-
CKRL3
CKRL2
CKRL1
CKRL0
Bit Number Bit Mnemonic Description
7 - 4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3:0
CKRL3:0
Clock Reload register
Prescaler1 value
F
ck_cpu
=[ 1 / 2*(16-CKRL)] * F
ck_XTAL1