PROASIC3E datasheet(10/37 Pages) ACTEL

10 / 37 page

I/O Structures in IGLOOe and ProASIC3E Devices

v1.4

I/O Registers

Each I/O module contains several input, output, and enable registers. Refer to Figure 5 for a

simplified representation of the I/O block. The number of input registers is selected by a set of

switches (not shown in Figure 3 on page 8) between registers to implement single-ended or

differential data transmission to and from the FPGA core. The Designer software sets these

switches for the user. A common CLR/PRE signal is employed by all I/O registers when I/O register

combining is used. Input Register 2 does not have a CLR/PRE pin, as this register is used for DDR

implementation. The I/O register combining must satisfy certain rules.

Notes:

1. All NMOS transistors connected to the I/O pad serve as ESD protection.

2. See Table 2 on page 3 for available I/O standards.

Figure 5 • Simplified I/O Buffer Circuitry

Programmable Input

Delay Control

Input Buffer Standard2

and Schmitt Trigger

Control

Input Signal to Core Logic

Input Buffer

(from core logic)

Output Signal

(from core logic)

Output Buffer

Logic and

Enable Skew

Circuit

Drive

Strength

and

Output

Slew Rate

Control

Clamp Diode

ESD Protection1

Weak

Pull-

Down

Control

(from

core)

Clamp Diode

ESD Protection1

VCCI

I/O PAD

Weak

Pull-Up

Control

(from

core)

Hot-Swap, 5 V Tolerance, and

Clamp Diode Control

Output Buffer

VCCI

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