Signetics Programmable Logic Devices - Al Kossow's Bitsavers

Signetics Programmable Logic Devices
Signetics Programmable Logic
Introduction
To control eech O-tenn. it is necessary to
IJnderstand that each control gate is a 36-lnput
AND gate. To make the 3-State buffer active
(Bx pin an output). the output of the control gate
must be at logic HIGH (1). This can be
accomplished in one of two ways. A HIGH can
be forced on all control gate input nodes. or
fuses can be programmed. When a fuse is
programmed. that-control gate input node is
internally pulled up to HIGH (1). See Figure 12
and Figure 13.
Programming the fuse permanently places a
HIGH (1) on the input to the control gate. The
input pin no longer has any effect on that state.
vee
1= HIGH(') 0---+---"'" 1= LOW (0) 0-=:::....+---......
A~:AYo---I.>-...... ---o8X=OUTPUT
A~:AY 0----11>-..... ---0 Bx = INPUT
Figure 12. Input Effect on Control Gates (Fuse Intact)
I=HIGH(')o---+---........
A~:AY 0---IJI~""--08x = OUTPUT
Figure 13. Effect on Control Gate If Fuse Is Programmed
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