ata6616 ATMEL Corporation, ata6616 Datasheet - Page 58

• Manufacturer Part Number: ata6616
• Description: Microcontroller With Lin Transceiver, 5v Regulator And Watchdog
• Manufacturer: ATMEL Corporation

4.5.3.3
4.5.3.4
4.5.3.5
4.5.3.6
4.5.3.7
58
ATA6616/ATA6617 [Preliminary]
Enable/Disable Clock Source
COUT Command
Clock Availability
System Clock Source Recovering
Clock Switching
The ‘Enable Clock Source’ command selects and enables a clock source configured by the set-
tings in the CLKSELR register. CSEL3..0 will select the clock source and CSUT1:0 will select the
start-up time (just as CKSEL and SUT fuse bits do). To be sure that a clock source is operating,
the ‘Request for Clock Availability’ command must be executed after the ‘Enable Clock Source’
command. This will indicate via the CLKRDY bit in the CLKCSR register that a valid clock source
is available and operational.
The ‘Disable Clock Source’ command disables the clock source indicated by the settings of
CLKSELR register (only CSEL3..0). If the clock source indicated is currently the one that is used
to drive the system clock, the command is not executed.
Because the selected configuration is latched at clock source level, it is possible to enable many
clock sources at a given time (ex: the internal RC oscillator for system clock + an oscillator with
external crystal). The user (code) is responsible of this management.
The ‘CKOUT’ command allows to drive the CLKO pin. Refer to
Buffer” on page 56
‘Request for Clock Availability’ command enables a hardware oscillation cycle counter driven by
the selected source clock, CSEL3..0. The count limit value is determined by the settings of
CSUT1..0. The clock is declared ready (CLKRDY = 1) when the count limit value is reached.
The CLKRDY flag is reset when the count starts. Once set, this flag remains unchanged until a
new count is commanded. To perform this checking, the CKSEL and CSUT fields should not be
changed while the operation is running.
Note that once the new clock source is selected (‘Enable Clock Source’ command), the count
procedure is automatically started. The user (code) should wait for the setting of the CLKRDY
flag in CLKSCR register before using a newly selected clock.
At any time, the user (code) can ask for the availability of a clock source. The user (code) can
request it by writing the ‘Request for Clock Availability’ command in the CLKSCR register. A full
polling of the status of clock sources can thus be done.
The ‘Recover System Clock Source’ command returns the current clock source used to drive the
system clock as per
updated with this returned value. There is no information on the SUT used or status on CKOUT.
To drive the system clock, the user can switch from the current clock source to any other of the
following ones (one of them being the current clock source):
1. Calibrated internal RC oscillator 8.0 MHz,
2. Internal watchdog oscillator 128 kHz,
3. External clock,
4. External low-frequency oscillator,
5. External Crystal/Ceramic Resonator.
for using.
Table 4-4 on page
50. The CKSEL field of CLKSELR register is then
DRAFT
Section 4.5.2.7 “Clock Output
9132A–AUTO–10/08