How many ProTalkQ PTQ-PDPMV1 can I use in my Quantum HotStandby (HSBY) system?

The first firmware version for the PTQ-PDPMV1 that supported HSBY was version 1.15.  That version and successive versions up until version 1.25 could support only one (1) PTQ-PDPMV1 module per HSBY CPU chassis.  Starting with version 1.25 and later, you can have up to four (4) PTQ-PDPMV1 modules per HSBY chassis.

Due to the way the Modicon Quantum HSBY system works, you will need to have the same number of PTQ-PDPMV1 modules in each chassis with each HSBY CPU.  In other words, if you put four (4) in one chassis, you must also have four (4) in the other chassis.  This is required because the PTQ-PDPMV1 modules can talk only to the CPU in the chassis in which they are installed.  They cannot talk to a CPU in another chassis, even if it is the primary CPU.