Read and write commands can be issued to SDRAM devices with or without auto-precharge. If the auto-precharge option is selected, the SDRAM device automatically closes (precharges) the bank being read from or written to at the end of the transaction. Any subsequent access to this bank does not require a precharge command from the DDR subsystem for the transaction to be closed.

The L_AUTO_PCH signal is used to issue read and write requests with auto-precharge to the SDRAM. For write requests, the L_AUTO_PCH signal is asserted along with the L_W_REQ signal, and for read requests, the L_AUTO_PCH signal is asserted along with the L_R_REQ signal. It is acceptable to permanently tie the L_AUTO_PCH signal input high or low, as shown in Figure 1 and Figure 2.

The auto-precharge option is useful in situations where the requested read or write addresses are random. With random address sequences, banks of the exact row required by a subsequent request may not be open. If auto-precharge is not used for the previous access to a bank, subsequent transactions to that bank require the bank to be closed (precharged), causing a delay in the transaction execution. If auto-precharge is used with the previous access to the bank, the bank is closed and ready to be opened to the desired row.