What this CP 340 does on the serial line
The Siemens 6ES7340-1CH02-0AE0 is a SIMATIC S7-300 CP 340 communications processor with one isolated RS 422/485 interface, designed for point-to-point serial links to printers, barcode scanners, or other serial devices in a control cabinet. It handles ASCII protocol up to 1 024 byte frames and the 3964 (R) protocol at the same buffer depth, with a top transmission rate of 19.2 kbit/s over cable runs up to 1 200 m.
Sourcing a discontinued S7-300 serial module
For BOM lines that still specify the 6ES7340-1CH02-0AE0, availability is through independent distribution and surplus channels.
Fit and environmental limits
The module draws 165 mA max from the 5 V backplane bus, dissipates 0.85 W max, and fits a 40 mm wide slot in the S7-300 rail. Connection is via a 15-pin sub-D socket for the RS 422/485 bus. The interface is isolated, which avoids ground-loop issues when the serial cable runs between cabinets or over long distances.