A serial buffer transports packets through queues capable of operating in a packet mode or a raw data mode. In packet mode, entire packets are stored in a queue. In raw data mode, packet header/delimiter information is not stored in the queue (only packet data is stored). Packets can be transferred out of a queue in response to a slave read request. The serial buffer constructs a packet header in response to the slave read request, and retrieves a specified amount of packet data from the selected queue. The serial buffer also transfers out packets as a bus master when a water level exceeds a water mark within a queue. The serial buffer constructs packet headers for these bus master transfers, which may be performed in a flush mode or a non-flush mode (in packet mode), or in a flush mode (in raw data mode).