6

3492A–PLD–12/05

ATF1502BE

2.

Programmable Pin-keeper Option for Inputs and I/Os

The ATF1502BE offers the option of programming each of its input or I/O pin so that pin-keeper

circuit can be utilized. When any pin is driven high or low and then subsequently left floating, it

will stay at that previous high or low level. This circuitry prevents unused input and I/O lines from

floating to intermediate voltage levels, which causes unnecessary power consumption and sys-

tem noise. The keeper circuits eliminate the need for external pull-up resistors and eliminate

their DC power consumption.

Figure 2-1 shows the pin-keeper circuit for an Input Pin and Figure 2-2 shows the same for an

I/O pin. The pin-keeper circuit is a weak feedback latch and has an effective resistance that is

approximately 50 k

Ω.

Figure 2-1.

Input with Programmable Pin-keeper

Figure 2-2.

I/O with Programmable Pin-keeper

50K

50K