18.3.4 Bidirectional Buffers

A500K bidirectional buffers have all the features of both the input buffers and the output buffers:

• 2.5 and 3.3 CMOS input voltage levels
• Optional pull-up resistor
• Optional PCI compliance with PCI 2.1 Component Specification (3.3 Voltage pad only)
• Selectable drive strengths
• Selectable slew rates
• Three-state functionality
• ESD protection circuitry
• Latch-up protection circuitry

Bidirectional Buffer Naming Conventions

The names for the bidirectional buffers are composed of up to the following seven parts:

• The name base IOB identifying the buffer as a bidirectional buffer
• An optional one character code (L) designating an active low enable input for the IOB output buffer part. The code is omitted for the active high enable input.
• The number code 25 or 33 indicating a 2.5 or 3.3 voltage level
• A two character code indicating low power pad voltage (LP)
• A code indicating the drive strength (2.5 Volt pad: L for 1 mA, H for 3.5 mA; 3.3 Volt pad: L for 5 mA and P for PCI compliant 10 mA). I/O macros which have *25LP* require VDDP of 2.5V, while *33* and *25* (no LP) require VDDP of 3.3V.
• A one character code indicating the slew rate (L for low 25 mA/ns, N for nominal 50 mA/ns, and H for high 100 mA/ns).
• An optional one character code (U) designating a pull-up resistor. When there is no resistor, this code is omitted.