IBM RT Series Hardware Reference Manual page 217

Internal This signal is output to bit 4 (Disable Internal Video
Drivers) of the Miscellaneous Output Register.
V OUT Vertical retrace output
Jl This pin is connected to auxiliary jack 1 on the rear
panel of the adapter.
G'OUT Secondary green output
B'OUT Secondary blue output
B OUT Blue output
G Green input
B Blue input
R OUT Red output
BLANK This is a composite horizontal and vertical blanking
signal from the CRTC.
FEAT 1 This signal is output to bit 6 (Feature Code 1) of
Input Status Register O.
G' /1 Secondary green/Intensity input
HIN Horizontal retrace input from the CRTC
14MHZ 14 MHz signal from the system board
EXT OSC External dot clock output
HOUT Horizontal retrace output
IBM Enhanced Graphics Adapter 77