sequential (28) shift direction

 https://wodewangzhishime.blogspot.com/2023/02/if-ipaddress133133-nathon-road.html

Ref:  https://wodewangzhishime.blogspot.com/2022/06/httpswodewangzhishime_8.html .

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Me: This picture is just my design. . In reality, it may not be like this. .

If the current of the commuator is flowing to the right, and, the cycle is at up, only the NPN is saturated. .

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Me: In this case, the output of Q can't left shift.

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John: If output of Q left shift, the commutator must be at the down cycle, and the current must flow to the left hand side, and the PNP must be saturated. . .That mean, the PNP receive a signal of zero.