How many PC/104 boards can be stacked?
As with so many questions, the answer is “It Depends”. Some PC/104 CPU manufacturers will only guarantee 5 or 6 cards in a stack, while others have tested their CPU modules with up to 10 boards or more. The answer depends on the amount of bus drive capability on the CPU as well as the bus loading of the add-on modules. A well-designed module presents a maximum of one load on any bus signal that it uses. A poorly designed one may leave out buffer ICs and present 2 or more loads on some lines, which limits the number of add-on modules that you can put on the stack without overloading the CPU. You will have to try your proposed configuration to know for sure. Ask the CPU manufacturer about their experience with their various CPU modules, and also ask the add-on module vendors about the bus loading of their modules. Sometimes, adding AC bus termination, as indicated in the PC/104 specification, will help ensure signal reliability on systems with large numbers of modules. Answer by Johnatha
