What is needed for a scanner to be found?

[Hans]

I'm curious, what is needed for a scanner to be found.

I have an ancient, but fully functional Canon scanner F4200. But Canon does not provide new drivers anymore for windows 10.
Nevertheless, some 1-2 Windows 10 update back, the scanner did run with NAPS2 and TWAIN, Now NAPS2 claims, there was no scanner around, despite it was plugged into USB and is powered on.

I try to understand a bit more, what is the systematic.
I understand, that NAPS2 provides a communication interface, to talk TWAIN.
So on the other side, someone must tell, here I am and I talk TWAIN too l
Who is this? Who is the one talking TWAIN? Is Windows 10 able to talk TWAIN? Is a driver required to remind Windows that, it should answer the question, if a TWAIN talking device is around?

I would be happy to listen to a story, sheding some light onto this situation. I could imagine, here are some people around, knowing more into depth, how this negotiation works and what protocl this comminication is folloing.

Thanks in advance
Hans

[Ben Olden-Cooligan]

TWAIN acts as an intermediary between applications like NAPS2 and scanner drivers from different manufacturers. You do need some kind of driver for this to work. It's possible you had an old version of the driver installed that stopped working due to an OS upgrade. I recommend trying to find and reinstall a driver.

Maybe the Windows 7 driver from here?
https://www.usa.canon.com/internet/portal/us/home/support/details/scanners/support-scanners-canoscan-series/canoscan-4200f?tab=drivers_downloads

[Hans]

Hi Ben

Perfekt !!
this was a short .... and very helpful ... information.

1) the installation of the old Windows 7 driver, was a very silent process, self executing, asking for nothing, but works perfectly!

2) for my understanding: A driver installed in the operating system is required. What does it provide? Does the driver

• tell the system, that a scanner is around
• make the interface between the hardware and the system using some kind of language Windows understands
• an Windows is the one, being able to talk TWAIN with the NAPS client

---

• or does the hardware already provide the ability to talk TWAIN and Windows just has to provide the ports to allow communication?

best regards
Hans

[Ben Olden-Cooligan]

The TWAIN architecture is like this:

Application (NAPS2) -> TWAIN Data Source Manager (DSM) -> TWAIN Data Source (Canon Driver) -> Physical scanner

When a TWAIN-compliant driver is installed, it tells the TWAIN DSM that it is a "data source" by putting a .ds file in the C:\Windows\twain_32 folder. When an application like NAPS2 wants a scanner, it asks the DSM, which asks all of its data sources if a scanner is connected.

Windows provides a base layer that the driver runs in and helps the driver communicate with the physical scanner (as it does with any kind of hardware driver). Windows also comes with a TWAIN DSM preinstalled.

[Hans]

Great Ben!

Just a short test, reassuring, if I understood the role of each component correctly

• Obligatorily Hardware and driver ** belong together they are one universe and it is a proprietary communication between them, in this case the driver inevitably must** be provided by Canon. The driver provides the interface between hardware and windows and transmits all commandys which will be translated to TWAIN commands usind the driver DLL in the C://Windows/TWAIN_32 folder

• The TWAIN Data Source Manager is provided by the operating system Windows 10 and it defines the soft-ports of the driver and the client. It checks which drivers are found in the C://Windows/TWAIN_32 folder

• NAPS2 provides the user-interface generating the TWAIN commands directed to the DSM, asking the DSM which device talking TWAIN is available and sending its TWAIN commands to the selected TWAIN device.

Is this correct?
Thank You
best regards
Hans

[Ben Olden-Cooligan]

Yes, that's right.

[Hans]

Thank You Ben, for checking my summary and giving answers to a beginner so patiently.