A Variable Node Processing Unit (VNPU) and a Check Node Processing Unit (CNPU) are designed in order to be used in Low Density Parity Check (LDPC) decoding by the Min-Sum Algorithm (MSA). The designed blocks are fully parallel and flexible to be used for different block length when a regular (3, 6) LDPC codes are required. The proposed VNPU and CNPU have been first designed and implemented in software using Simulink tool following a modular design approach. In a second step, these blocks were described and simulated using Very High Speed integrated circuits Hardware Description Language (VHDL). Comparison between these two implementations shows that the proposed high level methodology is efficient to test and validate digital circuits before being implemented on desired Field Programmable Gate Array (FPGA) device.