LVDS_33 support

在HR bank/HD bank中，支持LVDS的bank使用VCCO 3.3v供电，仅仅需要对端给过来的信号，满足标准的LVDS差模电压/共模电压的标准即可。如下截图：

 限制：

仅能作为input使用，无法作为output。

应用：

硬件上该bank VCCO接3.3V电压，实际vivado中IO电平标准设置为LVDS_25即可。下图为实际在vivado中验证通过的示例。

原理解释：

LVDS_18 LVDS_25 LVDS_33都仅仅是FPGA侧的称呼，区别就是VCCO电压的区别。对于ASSP/ASIC来说，仅有LVDS的说法。只需要信号特性满足LVDS的要求（主要是input/output的差模/共模电压等指标），互相均可以连接。

AR43989

3.3V LVDS:

• The "LVDS_33" I/O Standard that was available in some older FPGA families, is not supported in 7 Series, UltraScale or UltraScale+ devices.
• Neither High Range (HR) banks, High Density (HD) banks, nor High Performance (HP) banks can have their VCCO pins powered at 3.3V (if using LVDS outputs).
• Older families' LVDS_33 outputs might be supportable in the 7 Series, UltraScale and UltraScale+ I/O banks, but care must be used to ensure that:

1. Vin in Table 1 and 2 of the Data Sheet is not violated.
2. VIDIFF and VICM for LVDS (HP banks) or LVDS_25 (HR or HD banks) is not violated.

Running signal integrity simulations using IBIS models might be required in order to insure that those two items are not violated.