HDMP-0421

The HDMP-0421 is a Single Port Bypass Circuit (PBC) with Clock and Data Recovery (CDR), and dual Signal Detect (SD) capability. This configuration will control jitter accumulation while repeating incoming signals. Port Bypass Circuits are used to provide loops that are continuously on in hard disk arrays constructed in Fibre Channel Arbitrated Loop (FC-AL) configurations. Hard disks may be pulled out or swapped while other disks in the array are available to the system. This device may also be used in multi-initiator loop configurations. A Port Bypass Circuit is a 2:1 Multiplexer array with two modes of operation: DISK IN LOOP and DISK BYPASSED. In DISK IN LOOP mode, the loop goes into and out of the disk drive. Data go from the HDMP-0421's TO_NODE[n]± differential output pins to the Disk Drive Transceiver IC (for example, an HDMP-1536A) Rx± differential input pins. Data from the Disk Drive Transceiver IC Tx± differential output pins go to the HDMP-0421's FM_NODE[n]± differential input pins. Figures 4 and 5 show connection diagrams for disk drive array applications.

In DISK BYPASSED mode, the disk drive is either absent or non-functional and the loop bypasses the hard disk. DISK IN LOOP mode is enabled with a HIGH on the BYPASS[n] pin and DISK BYPASSED mode is enabled with a LOW on the same pin. Multiple HDMP-0421s may be cascaded or connected to other members of the HDMP-04xx family through the FM_LOOP and TO_LOOP pins to create loops for arrays of disk drives. See Table 2 to identify which of the two cells (0:1) will provide FM_LOOP, TO_LOOP pins (cell connected to cable). ALL TO_NODE outputs of the HDMP-0421 are of equal strength. Combinations of HDMP-04xx may be utilized to accommodate any number of hard disks.

The HDMP-0421 may also be used as a pair of 1=>1 buffers, one with a CDR and another without. For example, HDMP-0421 may be placed in front of a CMOS ASIC to clean the jitter of the outgoing signal (CDR path) and to better read the incoming signal (CDRless path).