Is it possible to interface an Apple IIe to a Commodore 1525 printer?
With the price of Commodore peripherals as low as they are, that's a tempting idea. However, it's not generally feasible. Commodore uses what is known as intelligent peripherals. In other words, the peripherals contain their own microprocessor, ROM and RAM, and thus are small microcomputers in their own right. The peripheral carries out its task under its own control, rather than being entirely controlled by the main computer. This allows for a very rudimentary form of parallel processing, freeing the computer for some other work while the peripheral is busy. Apple II-series machines, on the other hand, are designed to use so-called dumb peripherals which must be controlled by the computer. All instructions for the device are contained in memory, and the operation must be completed before the next step in the program can be executed.
Furthermore, Commodore serial peripherals (such as the 1525 printer) are not set up to operate with true RS-232 interfaces-the voltage levels are slightly different. That's why it's important to use an interface to generate the proper RS-232 voltage levels when using a non-Commodore peripheral on a Commodore computer.
Conversely, an Apple using a Commodore printer would need an interface to generate the levels that the Commodore printer is looking for, and a program to handle the interchanges of data between the computer and the printer.
Interfacing a Commodore printer to an Apple isn't impossible-in fact, early Apples were interfaced to almost everything imaginable. It's just extremely difficult without an extensive technical background.