  Self-dual Yang-Mills instantons on $R^4$ correspond to algebraic ADHM data.
The ADHM equations for $S^1$-symmetric instantons give a one-dimensional
integrable lattice system, which may be viewed as an discretization of the Nahm
equations. In this note, we see that generalized ADHM data for $T^2$-symmetric
instantons gives an integrable two-dimensional lattice system, which may be
viewed as a discrete version of the Hitchin equations.
