Modern USB/TCP connected PLCs just encapsulate RS-232 data into USB or TCP packets, nothing else (for backward compatibility). Also there are encapsulation and decapsulation devices which enables archaic PLCs and other industrial devices to be retrofitted to more modern systems.
Moreover, the OP noted that emulation speed was at critical importance so, the code is CPU speed sensitive. Missing specs, missing company, missing source plus time sensitivity makes this endeavor very risky if not hard.
Yep.
Modern USB/TCP connected PLCs just encapsulate RS-232 data into USB or TCP packets, nothing else (for backward compatibility). Also there are encapsulation and decapsulation devices which enables archaic PLCs and other industrial devices to be retrofitted to more modern systems.
Moreover, the OP noted that emulation speed was at critical importance so, the code is CPU speed sensitive. Missing specs, missing company, missing source plus time sensitivity makes this endeavor very risky if not hard.