I tried to use Putty to connect to my serial port test instrument (Agilent’s 33120A or E3600 series power supplies) and to my dismay it doesn’t respond to my commands.

I figured it might be newlines not being recognized properly. Checked the programming manuals and found that HP/Agilent accepts LF (‘\n’)as newline and optionally allowing a CR (‘\r’) before it (i.e. CR+LF like Windows).

I thought this configuration (Implicit LF in every CR) would work:

However it doesn’t! I had to dig through internet forums to find out that the ‘Terminal’ settings page controls what gets SPIT OUT TO THE TERMINAL SCREEN, not how your keystrokes are treated/sent! This page controls what your keystrokes mean:

However, it says nothing about what Putty does with ENTER key. I found from Stackflow that Putty sends out only CR (‘\r’) when ENTER key is pressed.

Turns out with terminals,

• Ctrl+J is LF
• Ctrl+M is CR,

and the convention for ENTER is Ctrl+M (also mentioned here):

So if you want ENTER/RETURN key to generate LF (instead of CR) with the official putty, you have to press Ctrl+J each time!

Putty sending CR (Ctrl+M) with ENTER key by default is also hinted by the default Telnet (only applies to telnet, not serial) setting in the Putty docs “Return key sends Telnet New Line instead of Ctrl+M”, which means outside Telnet, it the default behavior or ENTER/RETURN key is Ctrl+M (CR)!

Ironically even HyperTerminal came with the option to send out CR+LF on ENTER key! Luckily some kind soul (Grzegorz Niemirowski) compiled a mod (currently v0.74) which added the option and and posted it on Stack overflow: