The NVT uses 7 bit codes for characters, the display device, referred to as a printer, is only required to display the "standard" printing ASCII characters represented by 7 bit codes and to recognise and process certain control codes. The 7 bit characters are transmitted as 8 bit bytes with most significant bit set to zero. An end-of-line is transmitted as the character sequence CR (carriage return) followed by LF (line feed). If it is desired to transmit an actual carriage return this is transmitted as a carriage return followed by a NUL (all bits zero) character.
Note that NVT ASCII is used by many other Internet protocols.
The following control codes are required to be understood by the Network Virtual Terminal.
|Line Feed||LF||10||Moves the printer to the next print line,|
|keeping the same horizontal position|
|Carriage Return||CR||13||Moves the printer to the left margin|
|of the current line|
The following further control codes are optional but should have the indicated defined effect on the display.
|BELL||BEL||7||Produces an audible or visible signal|
|(which does NOT move the print head)|
|Back Space||BS||8||Moves the print head one character position|
|towards the left margin.|
|On a printing devices this mechanism|
|was commonly used to form|
|composite characters by printing two|
|basic characters on top of each other.|
|Horizontal Tab||HT||9||Moves the printer to the next horizontal|
|It remains unspecified how either party|
|establishes where such tab stops are located.|
|Vertical Tab||VT||11||Moves the printer to the next vertical|
|It remains unspecified how either|
|party determines or|
|establishes where such tab|
|stops are located.|
|Form Feed||FF||12||Moves the printer to the top of the|
|next page, keeping|
|the same horizontal position.|
|On visual displays|
|this commonly clears the screen and|
|moves the cursor to the top left corner.|
The NVT keyboard is specified as being capable of generating all 128 ASCII codes by using keys, key combinations or key sequences.