Answers Database LogiCORE PCI32 4000/Spartan: Are the XC4000XLT and Spartan devices 3.3V/5V PCI compliant? Record #5254 Product Family: Documentation Product Line: PCI Apps Product Part: PCI Frequently Asked Questions Problem Title: LogiCORE PCI32 4000/Spartan: Are the XC4000XLT and Spartan devices 3.3V/5V PCI compliant? Problem Description: Urgency: Standard General Description: Are the XC4000XLT and Spartan devices 3.3V/5V PCI compliant? Solution 1: XC4000XLT: The PCI specifications require that all devices have clamp diodes to ground for 5V and 3.3V PCI compliance. The 3.3V PCI specification also requires clamp diodes to 3.3V. The XC4000XLT devices achieve that through 8 power pins called Vtt and is in full compliance with the 3.3V PCI spec. See solution 3544 for more information on clamp diode specs. The upper clamp diodes protect the 4000XLT device in a 5V system. All 8 Vtt pins must be connected to 5V in order for the 4000XLT device to be 5V PCI compliant for upto 8 loads on the PCI bus. The 4000XLT does not have 5V PCI compliant drive strength for a fully loaded system, however the 3.3V drive strength is PCI compliant for a fully loaded system. I/O signaling compliance - Vtt connected to I/O compatibility ============================================== floating LVTTL, LVCMOS 5V LVTTL, TTL, LVCMOS, 5V PCI 3.3V LVTTL, LVCMOS, 3.3V PCI                (5V TTL/CMOS not allowed). ============================================== Solution 2: Spartan: The Spartan devices have an overshoot limiting ESD diode between every pin and Vcc and a similar symetrical diode to prevent undershoot below ground after a high-to-low transition. The Spartan devices are fully 5V PCI compliant, but not 3.3V PCI compliant and should never be connected to a 3.3V PCI bus. End of Record #5254 - Last Modified: 02/23/99 11:11

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