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Entry type: FAQ Entry ID: 41570, Entry date: 09/24/2001

Parallel interconnection of outputs with S7-21x and S7-22x

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Can I interconnect the DC outputs for the S7-21x and S7-22x CPUs in parallel.

CPU outputs are normal PNP transistors and should not be interconnected in parallel because of the asymmetry in the load and the different switch-on delays.

You can solve the problem by using a CPU 215, 216, 221, 222, 224, 226, 226XM or an EM223 expansion module.
All outputs of these units have FET transistors which can support a wired OR connection.


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