Can I switch the 15P PROM with a 20P PROM?

Any Vista-15P or Vista-20P version 2 or higher can be upgraded by removing the older version prom chip, and putting in a newer version prom. The prom chip is located slightly to the left of center in the board, and will have a white sticker showing the current version information. For example, you might see WA20P-5.2. This is a Vista-20P version 5.2.

Vista-15P and Vista-20P proms are virtually interchangeable. The only thing a prom can’t change, are the physical characteristics of the board itself. A Vista-20P has 8 hardwired zones, a Vista-15P only has 6. If you put a 20P chip into a 15P board, it will attempt to enable zones 7 and 8, in spite of the fact that they don’t physically exist. For this reason, they will need to be deleted from zone programming. If you put a 15P chip into a 20P board, you will lose zones 7 and 8, even though they do physically exist. For this reason, the physical zones should remain open, or strapped out with resistor. So, the answer is, yes, you can interchange prom chips between the Vista-15P and Vista-20P versions 2 or higher, but in either case, you will lose hardwired zones 7 and 8. For downloading purposes, the chip in the panel determines what you will choose as your panel type in Compass.