  We consider a spatially non-autonomous discrete sine-Gordon equation with
constant forcing and its continuum limit(s) to model a 0-$\pi$ Josephson
junction with an applied bias current. The continuum limits correspond to the
strong coupling limit of the discrete system. The non-autonomous character is
due to the presence of a discontinuity point, namely a jump of $\pi$ in the
sine-Gordon phase. The continuum models admits static solitary waves which are
called $\pi$-kinks and are attached to the discontinuity point. For small
forcing, there are three types of $\pi$-kinks. We show that one of the kinks is
stable and the others are unstable. There is a critical value of the forcing
beyond all static $\pi$-kinks fail to exist. Up to this value, the
(in)stability of the $\pi$-kinks can be established analytically in the strong
coupling limits. Applying a forcing above the critical value causes the
nucleation of $2\pi$-kinks and -antikinks. Besides a $\pi$-kink, the unforced
system also admits a static $3\pi$-kink. This state is unstable in the
continuum models. By combining analytical and numerical methods in the discrete
model, it is shown that the stable $\pi$-kink remains stable, and that the
unstable $\pi$-kinks cannot be stabilized by decreasing the coupling. The
$3\pi$-kink does become stable in the discrete model when the coupling is
sufficiently weak.
