Slot fit and protocol handling
The Siemens 6ES7138-4DF00-0AB0 is a current-production serial interface module for the ET 200S distributed I/O system, handling RS232, RS422, and RS485 with ASCII or 3964(R) protocol up to 19.2 kbps. The 15 mm width consumes one slot on the ET 200S terminal bus, and the module draws 1.2 W typical from the 24 V DC supply plus 10 mA from the backplane bus. The 7-byte send and receive buffer limits each serial message frame to 7 bytes – fine for small telegrams or parameter exchanges; larger payloads will need a different interface gateway. Protocol configuration includes ASCII with baud rates from 110 to 19.2 kbps, parity choices (none, odd, even, any), and 7 or 8 data bits with 1 or 2 stop bits.
In the panel, on the rail
This module mounts directly onto a compatible ET 200S base unit (BU type A0 or A1); the 52 mm depth and 81 mm height are standard for the family, so it sits flush with neighbours. The 1.2 W dissipation is low enough that no special ventilation is required – it runs cool even at 60 °C ambient in a densely packed cabinet. Wiring is handled by the base unit's spring-clamp terminals; the serial signals follow the pin assignments listed for RS232 (8 signals: TxD, RxD, RTS, CTS, DTR, DSR, DCD, PE –), RS422 (TxD(A/B), RxD(A/B), GND –), or RS485 (R/T(A/B), GND –).
First power-up checks
On initial power-up, verify the group-error SF LED (red –) stays off. If it lights, check backplane communication and 24 V DC supply. Set the protocol in the hardware configuration (STEP 7 or TIA Portal) – ASCII – and match the baud rate to the connected device (110 to 19.2 kbps). The module isolates the serial interfaces from the internal power supply, which helps avoid ground loops on long cable runs up to 1 200 m.
Sourcing this serial slice
Siemens lists this module as current production and a standard ET 200S catalog item. For BOM fill or a line-down swap, we source it through our Siemens direct channel. RFQ for lead time and quantity; module ships individually or in small lots.