More recent versions of Putty have serial as an option, and that is my preferred client. Regarding your problem, I would wonder if there is a flow control issue. Are you set to none, hardware (RTS/CTS), or software (XON/XOFF)? However you are set, try the other options and see if that helps.I doubt that is actually a problem with Tera Term. No idea on the firmware question.
I think if the flow control thing would be wrong, then i had NO access to the terminal... or only strange (binary etc.) characters.... i have access to the terminal, but i don't know what key i have to use to confirm the reset confirmation: y OR Y OR z OT Z ot whatever...?
On the IP config dialog (e.g. to set a static one) i was success ful to save - there i've found the key.
The RS232 params shold not be the problem - the question it more which terminal software is the most useable. and which terminal emulation? (-> I think VT100, right?)
I can't guarantee it, but my gut still tells me that this is mostly a serial issue. Terminal emulation mismatch (say the device expect a televideo terminal and you are doing vt100) would cause display scrambling when it tried to clear the screen or move the cursor around. It wouldn't cause it to not accept characters. Most things these days use 9600 baud, 8 data bits, no parity, and 1 stop bit. This device COULD be expecting something else which might cause some characters to not be recognized. It's been a long time since I had to deal with that kind of thing, but that seems a more likely cause to me.