DC Carry Chain, 6 Interconnected Diode Gates + 1 Inverter <UL> <LI><b>R181A</b> is a drawing of DEC's R181A.</LI> <LI><b>R181C</b> is a drawing of DEC's R181C.</LI> <LI><b>R181X</b> is a 'modernized' R181.</LI>