Operation Of The Clock Output Function - Fujitsu MB96300 series Hardware Manual

MB96300 Super Series Hardware Manual
23.3

Operation of the Clock Output Function

The clock output function can be used to output two independent clocks at the CKOT0/
CKOTX0 and CKOT1/CKOTX1 output pins. The clocks can be activated and deactivated
synchronously.
■ Activating the clock output function
Activate the clock output function for the CKOT0/CKOTX0 and CKOT1/CKOTX1 pins as follows:
• Configure the corresponding COCR register by selecting the requested clock and division value.
• Enable the CKOT and/or CKOTX output pin by setting the corresponding output enable bit to "1". The
start bit RUNC should be set to "1" at the same time or after setting the output enable.
The CKOT pins output "0" and the CKOTX pins output "1" directly after activating the output enable.
After setting the RUNC start bit to "1", the synchronization circuit is activated and starts outputting the
selected clock at the corresponding CKOT/CKOTX pins. Reading the RUNM bit now as "0" indicates that
the output clock is not yet started (synchronization mechanism is still in effect) and reading "1" means that
the output clock is started.
■ Disabling the clock output function
Disable the clock output function as follows:
• Stop the clock output by setting the RUNC bit to "0". This stopping is done by using the synchronization
circuit. Confirm that the clock is actually stopped by reading the RUNM bit (set to "0").
• When the clock is stopped, it is allowed to change the configuration of the COCR register or to disable the
resource output by setting the output enable bit to "0".
The output value at the CKOT/CKOTX pins after stopping the clock is again "0" for the CKOT pins and "1"
for the CKOTX pins.
The synchronization circuit for starting/stopping the output clock needs an active source clock. If the source
clock selected by the SEL[3:0] bits is disabled, then the status of the output clock cannot be changed. Setting
the RUNC bit to another value is possible, however the RUNM monitor bit will not change its value.
■ Changing the Clock Output Configuration Register contents
The COCR register should only be written if the corresponding clock output is stopped (RUNM is "0").
Otherwise a spike can be output.
CHAPTER 23 CLOCK OUTPUT FUNCTION
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