Encoder interface and data mapping
The 6ES7138-6BA01-2BA0 TM Posinput 1 module accepts incremental encoders with 5 V TTL push-pull outputs or RS-422 signals, and SSI absolute encoders with Gray or binary code, singleturn or multiturn. That covers the common encoder types on servo axes and linear actuators — one module for the position feedback loop, no separate converter needed. Input data is 16 bytes in normal mode, dropping to 4 bytes in Fast mode; output data is 12 bytes, with 4 bytes reserved for Motion Control. The Fast mode reduces the data payload for higher update rates when the application only needs basic position values.
Supply and signal levels
The module requires a 24 V supply on L+ with a -0.8 V drop allowance — standard for the ET 200SP backplane bus. The 5 V TTL input accepts push-pull encoders only, with a signal "1" threshold of +11 to +30 V and signal "0" at -5 to +5 V. The RS-422 input handles differential encoder signals up to 1 000 m with shielded cable. Switching times are 50 µs max both directions, and the monoflop time is parameterizable at 16, 32, 48, 64 µs or automatic. That 50 µs edge-to-edge timing keeps up with encoder pulse trains at moderate speeds — fine for conveyor position or spindle orientation.