Measurements of Z{sup 0} to Heavy-quark couplings at SLD

We present measurements of Z{sup 0} to heavy-quark coupling electroweak parameters, R{sub b}, R{sub c}, and parity-violation parameter A{sub c}, from SLD. The measurements are based on approximately 550k hadronic Z{sup 0} events collected in 1993-98. Obtained preliminary results of R{sub b} and R{sub c} measurements are R{sub b} = 0.2159 {+-} 0.0014 {+-} 0.0014 and R{sub c} = 0.1685 {+-} 0.0047 {+-} 0.0043. In the A{sub c} measurement, we use four methods to determine the initial-quark charge: combined Kaon charge and Vertex charge, lepton, exclusively reconstructed D*, D-mesons, and a new method using inclusive soft-pion from D*. The preliminary results of these four methods were combined to give A{sub c} = 0.634 {+-} 0.027