Table 4-3 Level 1-Level 2 Compatibility Comparison
Difference Area Level 1
(VT100 Mode)
Level 2
(VT200 Mode)

Sends ASCII only.

Keystrokes that normally send DEC Supplemental Characters transfer nothing. (Interpreted as an error.)

User-defined keys are do not operate.

Special function keys and six editing keys do not operate (except F11, F12, and F13, which send ESC, BS, and LF, respectively).

Permits full use of VT220 keyboard.
7 or 8 bits The 8th bit of all received characters is set to zero (0). The 8th bit of all received characters is significant.
Character Sets Only ASCII, national replacement characters, and DEC special graphics are available. All VT220 character sets are available.
C1 Control Characters All transmitted C1 controls are forced to S7C1 state and sent as 7-bit escape sequences.