In Spartan-3A, there are banking rules when using the TMDS and LVPECL_33 I/O standards that are not checked for in the ISE 9.1.01i design tools or documented in the data sheet.
Spartan-3A supports the use of both TMDS and LVPECL_33 I/O standards. However, the following rules are not caught in the current ISE software; these are also not documented in the Spartan-3A Data Sheet (DS529, v1.1):
- TMDS inputs require VCCAUX = 3.3V. VCCO: does not matter.
- TMDS outputs require VCCO = 3.3V (and must be in bank 0 or 2). VCCAUX: does not matter.
- LVPECL_33 inputs require VCCAUX to be 3.3V.
The above setups are required and supported when using TMDS or LVPECL_33 I/O standards. Any other setup is not supported and could result in incorrect behavior in the I/O.
Any of the other 3.3V standards, single-ended or differential, can use VCCAUX = 2.5V or 3.3V. The ISE software will be fixed to check for the above I/O standard rules, and will error out if they are violated. The fix is scheduled to be in the ISE 9.2i software release. The next release of the data sheet will be updated with this information, as well.
Consult the Spartan-3A Data Sheet for more information: