Systems and methods for enabling a slave device to generate a tag that is an index into a buffer where the slave device stores information related to an active transaction such as a write command received by a master device. The tag is sent to the master device with a reply (such as a response to a write command received from the master device), the master device returns the tag with the data to be written to the slave device. The slave device can efficiently associate the received data with the previously sent write command by retrieving the command from the buffer using the tag as an index into the buffer. Additional hardware such as a content-addressable memory unit is not required to make the association.