It could fire in the middle of a message and you could only get half of the message. It does not even log control characters that it does not act on.I think you are close, you just need to realize that the DataReceived event fires somewhat randomly. Tera Term 4.94 (20170228) does not show control characters. It has a unique interpretation of CR: it goes to home position but does not linefeed until a character comes in. (Stark red and yellow.) Stark yet cluttered user interface.

It color codes local echo and incoming text (good). RealTerm 2.0.0.70 (20130828) shows all control characters, as 2-digit codes or as symbols like ␂, using included custom fonts. (Typing Ctrl+^ doesn't work.) These match the VISCII code table in Wikipedia. Ctrl+B displays as 'Ẳ' becomes ' ┐', which copies and pastes as ␂.Ĭtrl+E displays as 'Ẵ' becomes '│', which copies and pastes as ␅.Ĭtrl+F displays as 'Ẫ' becomes '─', which copies and pastes as ␆.Ĭtrl+T displays as 'Ỷ' becomes '¶', which copies and pastes as ␔Ĭtrl+Y displays as 'Ỹ' becomes '├', which copies and pastes as ␙.Ĭtrl+^ displays as 'Ỵ' becomes ' ' (whitespace), which copies and pastes as ␞. However, newly received control characters go back to not displaying anything, and Ctrl+E triggers answerback (PuTTY acts as if you typed 'PuTTY'). With these characters onscreen, if you then change 'Translation' to any other character set, the ẲẴẪỶỸỴ change to six other characters, which copy and paste as the actual control codes. Ctrl+BEFTY^ display as the hard-to-distinguish Vietnamese characters ẲẴẪỶỸỴ, and copy and paste as the same. That makes PuTTY show six control characters onscreen, but only because VISCII defines those six as printing characters. PuTTY 0.69 (20170424) does not show control characters, except if, under 'Translation', 'Remote character set', you select 'VSCII'. Meanwhile, you can get very limited use from PuTTY, or use something else. For each control character, it could display a symbol, take an action, or both. Or add options that control how it handles common control characters for which it has actions (CR, LF, BEL, BS, FF (clear), ^E (answerback), etc.) and uncommon control characters for which it has no actions. It seems very doable: just create a custom character set that defines most of 0x00-0x1F as printable characters.

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