This information is edited from a repost of an acig.org forum post by mrdetonator:
http://www.secretprojects.co.uk/forum/index.php/topic,25.msg59.html#msg59
The main radar operating switch "БСВ-СЦ-R-BСМВ" chooses between two radar main operating modes.
The position БСMV switches among БСВ, БСВ-ΔH4, БСВ-ΔH1, СМВ and МВ. In the БСВ-СЦ position the radar switches between the БСВ-СЦ and МВ modes
The SIST switch has 5 operating modes: "R", "T-R", "T", "T-phi0", "NAV".
„R“ mode determines the onboard radar as a main targeting system.
Also during ground attack the radar can measure distance to the target.
„T-R“ mode means cooperation between the radar and the IRST, if the radar is jammed the IRST can pick up the target distance and vice-versa.
The „T“ mode prioritizes the IRST as a main targeting system.
Also this mode is used in case of radar damage or hidden approach. The S-23E radar works in so called quasi-scan mode.
The radar antenna is slaved to IRST sensor and is providing the data for the launch of R-23T.
„T-phi0“ mode the R-23T missile seeker is caged to the axis of the plane.
„NAV“ mode is for navigation flights under RSBN, or “return to base” command (VOZVRAT).
The HUD display is showing “K”(curse), “G”(inclination) symbols, which the pilot has to follow.
The switch IZL-EKV-VYK impulse transmitter (emit/equivalent/off)
The switch NAVED-AVT-RUCHN, the instrument guiding by datalink ARL-SM on/off
The switch MSKC-PPS-ZPS, low-speed target engagements (<500km/h)/front/rear hemisphere.
If no jamming occurs, the MSKC switch position allows the radar to detect targets with any closure speeds.