Differences between I/O signals at D-Sub and P12 connectors

The control input and status output signals of the NSP series nonstop power supplies are provided in form of RS232C signals at D-Sub connector and TTL level signals at P12 connector on output cable harness.
The definition and logic levels of each signal are introduced in FAQ, which you can access from HERE.

The differences in electrical characteristics and I/O circuit configuration between the RS232C and TTL signals are explained below:
Figure 1 shows the basic block diagram of the interface circuitry.

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Figure 1. Block diagram of RS232C and TTL signal Interface

The logic control section inside the power supply performs its tasks with TTL level input/output signals (High = 5 V, Low = 0V). The TTL signals are converted into RS232C logic levels by an RS232C driver (corresponding to ANALOG DEVICES ADM232AARN) inserted between the logic control section and D-Sub connector. Accordingly, you cannot mix the use of TTL and RS232C signals in system integration and application of the power supply.