Hi,

The VCO LM566 provide the TTL square wave output,
| IC | VOH (V) |
VOL (V) |
| LM566 | 14.27 | 6.41 |
Which is provided to CD4070 and CD4013's CLK,
| IC | VIH (V) |
VIL (V) |
| CD4013BE | 11 | 4 |
| CD4070BE | 11 | 4 |
whereas, the VIL is exceeding the range, but still the expected output is observed.
We need to Understand, how it is possible?
Regards,
Mirthunraju M