Block Diagram; Scsi Interface; Ram Buffer; Disk Controller - HP C2246 Technical Reference Manual

Block Diagram
Refer to figure 3-3. The drive electronics/controller PCA controls the operation of the drive,
including head positioning, data transfer, spindle speed, and power distribution.
SCSI Interface
The SCSI interface is the direct electrical interface between the SCSI channel and the drive
electronics. It handles all SCSI timing and protocol, and transfer of commands, status and
configuration information.
The SCSI interface handles SCSI protocol without intervention from the microprocessor,
and is capable of automatically controlling the proper sequence of bus phases involved in
each transaction. Full arbitration and disconnect/reselection are implemented by the SCSI
interface.
RAM Buffer
The RAM buffer contains 256-kilobytes of static RAM. All data transferred between the host
and the disk must pass through the RAM buffer.
Disk Controller
The disk controller coordinates the flow of data by interleaving RAM accesses between the
SCSI interface and the disk controller. It contains a DMA section which controls the transfer
of data between the SCSI interface, the buffer RAM and the disk controller. The DMA
accesses the 256-kilobyte static RAM buffer to match the transfer speeds of the SCSI interface
and the disk controller.
The disk controller also performs error checking on data being transferred from the disk to the
RAM buffer and generates ECC on data transferred from the RAM buffer to the disk. The
data controller also does header verification during read/write operations.
Data EncoderjDecoder
The primary function of the Data Encoder/Decoder is to convert between the NRZ (Non
Return to Zero) data/ clock present on the SCSI channel and RLL (Run Length Limited,
1,7) data transferred to and from the disk surface. This includes sector length and content
information provided by the host during format operations as well as data transfers during
normal Read and Write operations.
Microcontroller
The microcontroller used on the drive electronics/ controller PCA is a single-chip device. The
microcontroller is responsible for decoding incoming SCSI commands, controlling the servo
processor and the read/write circuitry, and managing the head alignment function.
3·8 Product Features
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