AT89C51ID2-SMSIM ATMEL [ATMEL Corporation], AT89C51ID2-SMSIM Datasheet - Page 15

• Manufacturer Part Number: AT89C51ID2-SMSIM
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

Oscillators
Overview
Registers
4289A–8051–09/03
Two oscillators are available for CPU:
•
•
Several operating modes are available and programmable by software:
•
•
In order to optimize the power consumption and the execution time needed for a specific
task, an internal prescaler feature has been implemented between the selected oscilla-
tor and the CPU.
Table 15. CKSEL Register
CKSEL - Clock Selection Register (85h)
Reset Value = 0000 000’HSB.OSC’b (see Hardware Security Byte (HSB))
Not bit addressable
Number
OSCA used for high frequency: Up to 40 MHz
OSCB used for low frequency: 32.768 kHz
to switch OSCA to OSCB and vice-versa
to stop OSCA or OSCB to reduce consumption
Bit
7
-
7
6
5
4
3
2
1
0
Mnemonic Description
CKS
Bit
6
-
-
-
-
-
-
-
-
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
CPU Oscillator Select Bit: (CKS)
Cleared, CPU and peripherals connected to OSCB
Set, CPU and peripherals connected to OSCA
Programmed by hardware after a Power-up regarding Hardware Security Byte
(HSB).HSB.OSC (Default setting, OSCA selected)
5
-
4
-
3
-
2
-
AT89C51ID2
1
-
CKS
0
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