®
DEVICE
SPECIFICATION
2.5 GBIT PORT BYPASS CIRCUIT FOR FIBRE CHANNEL ARBITRATED LOOP
2.5 GBIT PORT BYPASS CIRCUIT FOR FIBRE CHANNEL ARBITRATED LOOP
S2091
S2091
FEATURES
• Supports 2.5 Gbps Data Rates
• Fully differential for minimum
jitter accumulation
• TTL Bypass Select
• High speed 50Ω source terminated outputs
• 0.4W Typical power dissipation
• 3.3V power supply
• 20 Pin TSSOP
functional and data bypasses to the next available disk
drive. Normal mode is enabled with a High on the SEL
pin and Bypass mode is enable by a Low on the SEL
pin. Direct Attach Fibre Channel Disk Drives have an
“LRC Interlock” signal defined to control the SEL func-
tion. A system diagram showing the S2091 in a single
loop of a disk array is illustrated in Figure 2.
The S2091 can be cascaded with the S3040 (Data
retimer) for arrays of disk drives greater than 4.
Table 1 is a truth table detailing the data flow
through the S2091. Figure 3 shows a timing diagram
of the data relationship in the S2091. The primary
AC parameter of importance is the deterministic jitter
or data eye degradation inserted by the port bypass
circuit. The design for the S2091 minimized jitter ac-
cumulation by using high bandwidth, low skew fully
differential circuits. This provides for symmetric rise
and fall delays as well as noise rejection.
GENERAL DESCRIPTION
The S2091 is a Port Bypass Circuit (PBC). A single
channel Fibre Channel PBC offers designers maxi-
mum flexibility in FC-AL disk architectures. The
S2091 is designed to minimize jitter accumulation by
providing a high bandwidth fully differential signal
path. Port Bypass circuits are used to provide resil-
iency in Fibre Channel Arbitrated Loop (FC-AL) ar-
chitectures. PBC’s are used within FC-AL disk arrays
to allow for resiliency and hot swapping of FC-AL
drives.
A Port-by-Pass Circuit is a 2:1 Multiplexer with two
modes of operations: Normal and Bypass. In Normal
mode, the disk drive is connected to the loop. In
Bypass mode, the disk drive is either absent or non-
Table 1. Truth Table
SEL1
0
1
OUT
IN
DDI
DDO
IN
IN
Figure 1. S2091 Block Diagram
DDO P/N
DDI P/N
SEL
1
IN P/N
0
PBC
OUT P/N
1
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
