Power law fluctuations and scale free spatial patterns are known to characterize steady state plastic flow in crystalline materials. In this Letter we study the emergence of correlations in a simple Frenkel-Kontorova (FK) type model of 2D plasticity which is largely free of arbitrariness, amenable to analytical study and is capable of generating critical exponents matching experiments. Our main observation concerns the possibility to reduce continuum plasticity to an integer valued automaton revealing inherent discreteness of the plastic flow.At the macroscale one usually assumes that crystalline materials flow plastically when averaged stresses exceed yield thresholds. At the microscale plasticity evolves through a sequence of slow-fast events involving collective pinning and depinning of dislocational structures. Classical engineering theory has been very successful in reproducing the most important plasticity phenomenology such as yield, hardening and shakedown [1], however, a fully quantitative link between the phenomenological theory and the microscopic picture of plasticity remains elusive. The main reason is that the phenomenological approach implies spatial and temporal averaging in the system with poorly understood long range correlations.The presence of such correlations have been confirmed by numerous experiments revealing intermittent character of plastic activity with power law statistics of avalanches and self similar structure of dislocation cell structures [2]. The emergence of power laws suggests that in plasticity the relation between the microscopic and the macroscopic models is more akin to turbulence than to elasticity [3,4]. Similar critical features of stationary nonequilibrium states have been observed in a variety other driven systems with threshold nonlinearity and rate independent dissipation including, for instance, tectonic faults, magnets, and superconductors [5]. The origin of scale free attractors in such systems is a subject of active research, in particular, the problem of classifying the universality classes remains largely open [6]. In this situation finding the minimal representation of each class which is amenable to rigorous analysis is of significant general interest.The experimental evidence of plastic criticality has been corroborated by several numerical models [7]. The two main microscopic approaches are discrete dislocation dynamics, accounting for dislocation interactions on different slip planes [8][9][10], and a pinning-depinning model dealing with plasticity on a single slip plane [11,12]. Different meso-scopic continuum models implying partial averaging have also been shown to generate power law statistics of avalanches with realistic exponents [4,13]. Since scale free dislocation activity is expected to be independent of either microscopic or macroscopic details, one can try to maximally simplify the underlying physics while still capturing the observed exponents and even characteristic shape functions [14]. Presently the only analytically tractable models of pl...