English to Russian Tech/Engineering Electronics / Elect Eng TV

В руководстве по эксплуатации телевизора:

TELETEXT Buttons

Sub-code
This is a toggle function between normal page request and sub-code mode. Actually a distinction can be made between 3 different modes:
--- Page request mode
--- Sub-code mode with invalid sub-code
--- **Sub-code mode** with valid sub-code
The first sub-code command will show the current sub-code. If this sub-code was valid, the second sub-code command will delete the current sub-code. When four sub-code digits are displayed, the sub-code is valid. When the displayed sub-code is invalid, the next key press will abandon the sub-code mode.