  We consider a fully directed self-avoiding walk model on a cubic lattice to
mimic the conformations of an infinitely long confined flexible polymer chain;
and the confinement condition is achieved by two parallel athermal plates. The
confined polymer system is under good solvent condition and we revisit this
problem to solve the real polymer's model for any length of chain and also for
any separation in between the plates. The equilibrium statistics of the
confined polymer chain is derived using an analytical calculations based on the
generating function technique. The force of the confinement, the surface
tension and the monomer density profile of confined chain is obtained. We
propose that a method of calculations is suitable to understand thermodynamics
of an arbitrary length confined polymer chain.
