This paper proposes a programmable high-performance architecture of datapath in the merged DRAM logic (MDL) for video signal processing. A model of a datapath in the programmable MDL is generated, and two basic parameters, total reguired clock cycles (TRCC) and DRAM access rate (DAR), are defined by analysis of the model. Design guidelines are suggested for the optimized video signal processor based on the modeling and analysis of the MDL, The inverse discrete cosine transform (IDCT) and motion compensation (MC) of the video signal processing are analyzed in the MDL architecture. Two measures, TRCC and DAR, are determined such that the data bandwidth between DRAM and logic is not a bottleneck in the MDL architecture. The efficient datapath is designed based on these design guidelines. The datapath has processing units (ALU, MAC, and Barrel Shifter) with splittabilities of data and multi-port SRAM, The maximum performance of the proposed datapath with 200-MHz clock frequency is 3.2 GOPS for 8-bit video signals, which can deal with decoding high-level (1920 x 1080) in MPEG, The proposed MDL architecture has 2.1-4.8 times higher performance compared with conventional dedicated hardware chips. It can also be used for other multimedia signal processing due to its programmability.