Semiconductor memory devices, memory systems, and methods of operating the semiconductor memory devices

A semiconductor memory device includes a memory cell array, an error correction code (ECC) engine, an input/output (I/O) gating circuit, and a control logic circuit. The memory cell array includes a plurality of bank arrays, and each of the bank arrays includes dynamic memory cells. The control logic circuit generates a first control signal to control the I/O gating circuit and a second control signal to control the ECC engine, in response to an access address and a command. The control logic circuit controls the ECC engine to perform s-bit ECC encoding on a write data to be stored in a first page of at least one bank array, in response to a first command, and controls the ECC engine to perform t-bit ECC decoding on a first codeword read from the first page, in response to a second command.