What it is and what it fits
The Siemens 6AG1137-6AA01-7BA0 is a CM PtP (point-to-point) serial communications module for the ET 200SP distributed I/O system. It handles RS232, RS422, and RS485 on a single 15 mm wide slice that mounts on a BU type A0 base unit. Rated for 24 VDC with reverse polarity protection and draws 35 mA max. Transmission rate tops at 115.2 kbit/s, configurable parity, stop bits, bits per character. Telegram buffer holds 4 kbyte; performance mode: receive 24 byte, send 30 byte max. Cable length up to 1 200 m on RS485.
Field notes: wiring, diagnostics, and side-channel checks
Push-in terminals connect without tools; DIAG LED (green/red) signals health, RxD and TxD green LEDs show line activity. RS232 auxiliary signals (RTS, CTS, DTR, DSR, RI, DCD) support handshaking. Diagnostic alarm and wire-break detection are built in. Isolation tested at 707 V DC type test — enough for panel-to-panel separation. The 0.7 W typical power loss leaves headroom on the backplane.