HDMP-0440

The HDMP-0440 is a Quad Port Bypass Circuit (PBC), which provides a low-cost, low-power physical-layer solution for Fibre Channel Arbitrated Loop (FC-AL) disk array configurations. By using a PBC such as the HDMP-0440, hard disks may be pulled out or swapped while other disks in the array are available to the system.

A PBC consists of multiple 2:1 multiplexers daisy chained together. Each port has two modes of operation: "disk in loop" and "disk bypassed." When the "disk in loop" mode is selected, the loop goes into and out of the disk drive at that port. For example, data goes from the HDMP-0440's TO_NODE[n]± differential output pins to the Disk Drive Transceiver IC's (e.g. an HDMP-1636A) Rx differential input pins. Data from the Disk Drive Transceiver IC's Tx differential outputs goes to the HDMP-0440's FM_NODE[n]± differential input pins.

Figure 2 shows connection diagrams for disk drive array applications. When the "disk bypassed" mode is selected, the disk drive is either absent or non-functional and the loop bypasses the hard disk. The "disk bypassed" mode is enabled by pulling the BYPASS[n]- pin low. Leave BYPASS[n]- floating to enable the "disk in loop" mode. HDMP- 0440s may be cascaded with other members of the HDMP- 04XX/HDMP-05XX family through the appropriate FM_NODE[n]± and TO_NODE[n]± pins to accommodate any number of hard disks (see Figure 3). The unused cells in the HDMP-0440 may be bypassed by using pulldown resistors on the BYPASS[n]- pins for these cells. An HDMP-0440 may also be configured as five 1:1 buffers, as two 2:1 multiplexers or as two 1:2 buffers.