China DOS Union

Recently, the boss needs us to develop a software to intercept serial and parallel port data under the DOS operating system. I have no ideas at all. I hope everyone can give some suggestions on how to start.

The boss is testing your ability, right! Intercepting serial and parallel port data involves understanding hardware. First, familiarize yourself with computer hardware. For example, the addresses of serial and parallel ports are the same all over the world. Once you know the address, you can perform read and write operations on it.

The serial data port is not an IO port that can read the previous data. So, a solution idea is to externally connect a hardware similar to a watchdog on the serial port to collect data, and then read back from this hardware when there is no data transmission.
It is also possible to enter protected mode and set the IO of the serial port as a privileged instruction (the IO of the serial port in Windows is not a privileged instruction) to intercept, but it is too difficult and far less intuitive than the previous method.

DOS that thing is powerful

The boss is testing you, not using DOS but using Windows is better

Don't know what the boss wants to do with the DOS system

Although it doesn't make much sense to answer this question now, the part of the function the original poster needs can probably be achieved through the I/O capture function of Emm386. As for whether the function of intercepting data can be achieved, I need to look at the documentation in detail.