AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 50

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

USB Interface Clock
Registers
50
AT8xC5122/23
The USB Interface uses two clocks :
Table 24. Clock Selection Register - CKSEL (S:85h)
Reset Value = XXXX XXX0b
Table 25. Clock Reload Register - CKRL (S:97h)
Reset Value = XXXX 1111b
Bit Number Bit Mnemonic Description
Bit Number Bit Mnemonic Description
–
–
7 - 4
7:1
3:0
7
7
-
-
0
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.
CKRL3:0
6
6
-
-
CKS
-
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
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.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Clock Reload register
Prescaler1 value
F
ck_cpu
5
5
-
-
=[ 1 / 2*(16-CKRL)] * F
4
4
-
-
CKRL3
3
3
-
ck_XTAL1
CKRL2
2
2
-
CKRL1
1
1
-
4202D–SCR–06/05
CKRL0
CKS
0
0