attiny167-esxz ATMEL Corporation, attiny167-esxz Datasheet - Page 30

• Manufacturer Part Number: attiny167-esxz
• Description: 8-bit Avr 8-bit Microcontroller Microcontroller With 16k Bytes In-system Programmable Flash And Lin Controller
• Manufacturer: ATMEL Corporation

4.2.7
4.3
4.3.1
4.3.2
4.3.2.1
30
Dynamic Clock Switch
ATtiny167
Clock Output Buffer
Features
CLKSELR Register
Fuses Substitution
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to
36
If not using a crystal oscillator, the device can output the system clock on the CLKO pin. To
enable the output, the CKOUT Fuse or COUT bit of CLKSELR register has to be programmed.
This option is useful when the device clock is needed to drive other circuits on the system. Note
that the clock will not be output during reset and the normal operation of I/O pin will be overrid-
den when the fuses are programmed. If the System Clock Prescaler is used, it is the divided
system clock that is output.
The ATtiny167 provides a powerful dynamic clock switch circuit that allows users to turn on and
off clocks of the device on the fly. The built-in de-glitching circuitry allows clocks to be enabled or
disabled asynchronously. This enables efficient power management schemes to be imple-
mented easily and quickly. In a safety application, the dynamic clock switch circuit allows
continuous monitoring of the external clock permitting a fallback scheme in case of clock failure.
The control of the dynamic clock switch circuit must be supervised by software. This operation is
facilitated by the following features:
•
•
•
At reset, bits of the Low Fuse Byte are copied into the CLKSELR register. The content of this
register can subsequently be user modified to overwrite the default values from the Low Fuse
Byte. CKSEL3..0, SUT1..0 and CKOUT fuses correspond respectively to CSEL3..0, CSUT1:0
and ~(COUT) bits of the CLKSELR register as shown in
for details.
Safe commands, to avoid unintentional commands, a special write procedure must be
followed to change the CLKCSR register bits
Exclusive action, the actions are controlled by a decoding table (commands) written to the
CLKCSR register. This ensures that only one command operation can be launched at any
time. The main actions of the decoding table are:
–
–
–
–
–
–
Command status return. The ‘Request Clock Availability ’ command returns status via the
CLKRDY bit in the CLKCSR register. The ‘Recover System Clock Source ’ command
returns a code of the current clock source in the CLKSELR register. This information is used
in the supervisory software routines as shown in
‘Disable Clock Source’,
‘Enable Clock Source’,
‘Request Clock Availability’,
‘Clock Source Switching’,
‘Recover System Clock Source’,
‘Enable Watchdog in Automatic Reload Mode’.
(See Section “4.5.3” on page
Section 4.3.7 on page
Figure 4-5 on page
”System Clock Prescaler” on page
32.
31.
38.):
7728A–AUTO–07/08