7

0425H–PLD–3/11

Atmel ATF16V8C

11.

Security fuse usage

A single fuse is provided to prevent unauthorized copying of the ATF16V8C fuse patterns. Once programmed, fuse verify

and preload are inhibited. However, the 64-bit user signature remains accessible.

The security fuse will be programmed last, as its effect is immediate.

12.

Input and I/O pin-keeper circuits

The ATF16V8C contains internal input and I/O pin-keeper circuits. These circuits allow each ATF16V8C pin to hold its

previous value even when it is not being driven by an external source or by the device’s output buffer. This helps insure

that all logic array inputs are at known, valid logic levels. This reduces system power by preventing pins from floating to

indeterminate levels. By using pin-keeper circuits rather than pull-up resistors, there is no DC current required to hold the

pins in either logic state (high or low).

These pin-keeper circuits are implemented as weak feedback inverters, as shown in the Input Diagram below. These

keeper circuits can easily be overdriven by standard TTL- or CMOS-compatible drivers. The typical overdrive current

required is 40μA.

Figure 13.

Input diagram

Figure 14.

I/O diagram