Be careful. the Turbochannel MFB has nothing at all to do with
the mono version of the 2100/3100 cfb, which is also called
an mfb.

The 2100/3100 mfb uses the same basic hardware as the 3100 colour
display, but with an 8x smaller VRAM and outputs one bit per pixel,
with eight pixels per byte.

The PMAG-AA `mfb' has scanlines that start on 2048-byte boundaries,
with 1280 visible one-bit pixels per line, one pixel per byte.
Trying to use the same code to set up both may be a losing idea.

If it helps any, the DEC product servers and X11R6 (Xws-based Xdec
server) said the PMAG-AA was staticgray, 8 bits deep....

(PS: ive deliberately avoided words like `plane')