Knowledge Base / Schneider In-chassis

The order of bits in the Binary Inputs and Outputs of my PTQ-DNP module appear to be the opposite of what I expect. Why?

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When transferring Binary Inputs and Outputs to or from a Modicon Quantum CPU using the PTQ-DNP module, the bit pattern appears to be reversed, most-significant to least significant and vise versa.  In other words, to set DNP BI point 0, you have to set bit 15 in the 4X Holding Register and when you want to set DNP BI point 15, you have to set 4X Holding Register bit 0, and all the other bit positions in between seem to flip, too.

This is a quirk common to Quantum processors.  Within Quantum logic, if you copy a series of 0X or 1X bits to 4X registers, you will see the same type of apparent bit pattern reversals.  The backplane driver for the PTQ module copies the module's internal 16 bit registers to 3X registers in the Quantum State RAM or from 4X registers to the PTQ.  During this backplane copy process, the Quantum reverses the order of bits.