Reference Clock Limits For Detecting A Missing Clock - Texas Instruments Concerto F28M36 Series Technical Reference Manual

Safety Features
11. On the control subsystem, the CLOCKFAIL signal is also fed to TZ5n trip signal of all the PWM
modules. This allows the PWM outputs to trip in case of clock failure.
12. When a missing clock condition is detected, the counters are disabled. They need to be re-enabled by
software after all error handling and when a proper clock source is available again
NOTE: [1]On a clock fail condition, nothing is done in hardware to enter standby mode on the C28
side. When a CLOCKFAIL NMI is generated, the C28 application software should configure
the LPMCR registers to enter standby mode.
[2]Changing the clock limit values (REFCLKLO and HI limit) should be done after disabling
the missing clock NMI, using the MCLKNMIEN bit in the MCLKEN register. After the
registers are programmed for appropriate input clock frequencies, the MCLKNMIEN bit
should be set again after at least a 900ns delay.
[3]At power up, the circuit only checks whether the clock is ticking or not because the limits
encompass the entire range of clock input frequencies allowed in the device.
Example of clock limit register configuration: Internal Oscillator is at 10 MHz; 3-bit 10 MHz clock
counter overflows every 800ns.
Ref Clock Frequency
4 MHz (250ns)
10 MHz (100ns)
20 MHz (50ns)
100 MHz (10ns)
122
System Control and Interrupts
Table 1-15. Reference Clock Limits for Detecting a Missing Clock
Copyright © 2012–2019, Texas Instruments Incorporated
REFCLKLOLIMIT
0x3
0x7
0xF
0x4E
SPRUHE8E – October 2012 – Revised November 2019
www.ti.com
REFCLKHILIMIT
0x4
0x9
0x11
0x52
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