Download the latest CS203 low-level API package from the following location:
RFID firmware to v1.3.85 or above
TCP firmware to v2.18.0 or above
Instruction and product specifications are also being attached.
The low-level API package includes source code in C intended to be run on Linux-based host with gcc compiler. However, you can also cross-compiled to run on Windows-based platform with Cywin or similar toolchain.
Java code-snippet for accessing the low-level API with Java. This is based on a Windows-based NetBeans project.