20:07
TE - talk enable - when sending data TE must be High
PE - pull up enable - always LOW
SC - If you are BUS master. When you GRiD Compass is master and you are emulatin FDD (or whatever peripheral), SC must be LOW. Basically SC control IFC and REN pins on bus. Can bu useful if RPI become master and want to dump Yuri's 10 MB HDD.
DC - don't know for now. Will check little later. Related to control lines like EOI, ATN, NDAC, DAV, NRFD.