AR# 40268


Virtex-6 HXT - Top/Bottom Half Center Point is Asymmetric for the HX255T and HX250T Devices


Why is it that the Mixed-Mode Clock Manager (MMCM) in the bottom half of the Virtex-6 HX255T cannot route to the BUFG that is also in the bottom half of the device, for example, the BUFGCTRL_X0Y8?


The Virtex-6 HX255T is a die that is derived from the Virtex-6 HX380T.What this means is that the HX255Tuses the HX380T design, but removes some of the clock regions on the bottom of the device to make a smaller device.

The HX380T has nine clock regions with fivebelow the center of the device and four clock regions above the center of the device.For the HX255T, the bottomthree clock regions from the HX380T design are removed so that there are now four clock regions above the center and twoclock regions below the center.

Becausethis is an uneven split of the device, it appears that the MMCM is in the center of the device.In reality, the MMCM is in the top half and cannot reach the BUFGs in the bottom half of the device.

Similarly, the HX250T is derived from the HX380T, but without the three clock regions from the top of the device, which results in the HX250T having one clock region on top and five clock regions on the bottom.

AR# 40268
Date 12/15/2012
Status Active
Type General Article
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