SCSI Commands: 31BREAD BUFFER Page 1413.19 READ BUFFERThe READ BUFFER command reads data from the memory on the drive and sendsit to the initiator. This command is used in conjunction with the WRITE BUFFERcommand as a diagnostic function for testing the drive buffer memory andconfirming the SCSI bus or Fibre Channel interface integrity. The tape is notaccessed during execution of this command.3.19.1 READ BUFFER Command Descriptor BlockByteBits7 6 5 4 3 2 1 00 Operation Code (3Ch)1 Ignored LUN Mode2 Buffer ID3 (MSB)45Buffer Offset(LSB)6 (MSB)78Allocation Length(LSB)9 Control3.19.1.1 READ BUFFER Command Field DescriptionsField Bytes Bits DescriptionOperationCode0 The operation code for READ BUFFER is 3Ch.IgnoredLogical Unit1 5-7 The LUN field is vestigial from the SCSI-1 standard and is ignored.Mode 1 0-4 00h = Return descriptor and data.01h = Return Medium Auxiliary Memory (MAM), EEPROM orFLASH data.02h = Return data only.03h = Return descriptor only.04h = Return trace buffer data.0Ah = Return echo buffer.0Bh = Return echo buffer descriptor.Buffer ID 2 00h = normal access (default)54h = specifies access to MAMBuffer Offset 3-5 For Mode not equal 01h: The offset from the beginning of thespecified buffer in bytes.For Mode equal 01h: Set to the MAM page code as described inthe tables or FFFFFFh to specify the entire MAM.Note: Buffer Offset for FCP and SAS interface drives must have aMod 4 = 0 characteristic. I.e. must be evenly divisible by 4.AllocationLength6-8 Specifies the amount of data bytes to be returned. A value of 0 is avalid entry and returns no data.The drive stops sending data when the number of bytes specifiedhas been transferred or when all available data has been sent.Reserved All reserved bits must be 0.Control 9 See SCSI Command Control Byte Format on page 25.
