PAL
Volume Number: 1
Issue Number: 11
Column Tag: The Electrical Mac
Macintosh PAL Technology 
By Jeff Mitchell, President, Digital Solutions, MacTutor Contributing
PROGRAMMABLE LOGIC DEVICES
Among its other achievements, the Macintosh has stirred considerable interest
and spawned many rumors on the subject of PALs®. Most computer enthusiasts are
familiar with hardware terms like microprocessor, TTL, and UART. Programmable
logic, of which PALs are just one of several types, is a relatively recent phenomenon,
and hadn't received much attention from the general press until the Mac arrived with
its logic board full of it. It seemed as if everyone was convinced Apple had been able to
package some black magic in a mysterious device called a PAL.
My aim this month is to dispel the mystery surrounding PALs. I'll describe the
various types of programmable logic devices (PLD), detail their various internal
architectures, and explain what it is they actually do. I'll present an application which