SYNCHRONOUS DRAM HAVING TEST MODE WHERE AUTOMATIC REFRESH OPERATION CAN BE PERFORMED BY EXTERNAL ADDRESS AND AUTOMATIC REFRESH METHOD

摘要

PURPOSE: A synchronous DRAM is provided which can be automatically refreshed by accessing main cells and spare cells by an external address applied from the external in a test mode after establishing the test mode where main cells and spare cells can be automatically refreshed at the same time. CONSTITUTION: According to an automatic refresh method, word lines can be accessed by an external address applied from the external during an automatic refresh operation of a test mode, and main cells and spare cells can be accessed and automatically refreshed. In a synchronous DRAM, a mode register setting circuit(19) generates a mode register set signal by receiving a signal applied from the external in response to a plurality of control signals, during the automatic refresh operation of the test mode. An address selector(15) outputs the external address applied from the external to a memory cell array(11) in response to the activation of the mode register set signal during the automatic refresh operation of the test mode, and outputs an internal address to the memory cell array in response to the non-activation of the mode register set signal during the automatic refresh operation of a normal mode. Therefore, the word lines of the main cells and the spare cells of the memory cell array are sequentially accessed and refreshed by being controlled by the external address during the automatic refresh operation of the test mode.