Xilinx virtex-5 fpga

296 www.xilinx.com Virtex-5 FPGA User Guide
UG190 (v5.0) June 19, 2009
Chapter 6: SelectIO Resources
HyperTransport Protocol (HT)
The HyperTransport™ protocol (HT) also known as Lightning Data Transport (LDT), is a
low-voltage standard for high-speed interfaces. Its differential signaling based interface is
very similar to LVDS. Virtex-5 FPGA IOBs are equipped with HT buffers. Table 6-38
summarizes all the possible HT I/O standards and attributes supported.
Reduced Swing Differential Signaling (RSDS)
Reduced Swing Differential Signaling (RSDS) is similar to an LVDS high-speed interface
using differential signaling. RSDS has a similar implementation to LVDS in Virtex-5
devices and is only intended for point-to-point applications.
BLVDS (Bus LVDS)
Since LVDS is intended for point-to-point applications, BLVDS is not an EIA/TIA standard
implementation and requires careful adaptation of I/O and PCB layout design rules. The
primitive supplied in the software library for bidirectional LVDS does not use the Virtex-5
FPGA LVDS current-mode driver, instead, it uses complementary single-ended differential
drivers. Therefore, source termination is required. Figure 6-89 shows the BLVDS
transmitter termination.
Table 6-37: Allowed Attributes of the HT I/O Standard
Attributes
Primitives
IBUFDS/IBUFGDS OBUFDS/OBUFTDS
IOSTANDARD HT_25
DIFF_TERM TRUE, FALSE N/A
Table 6-38: Allowed Attributes of the RSDS I/O Standard
Attributes
Primitives
IBUFDS/IBUFGDS OBUFDS/OBUFTDS
IOSTANDARD RSDS_25
DIFF_TERM TRUE, FALSE N/A
X-Ref Target - Figure 6-89
Figure 6-89: BLVDS Transmitter Termination
ug190_6_83_030506
Z
0
= 50Ω
Z
0
= 50Ω
R
DIV
140Ω
R
DIFF
= 100Ω
R
S
165Ω
R
S
165Ω
IN
INX
Data in
-
+
BLVDS_25
IOB
BLVDS_25
BLVDS_25
IOB