11.5 External Memory Access

Not all of Microchip’s DSC devices have a parallel master port peripheral (see 11.4 Parallel Master Port Access [DD]), and not all memories are suitable for attaching to the PMP (serial memories sold by Microchip, for example). The toolsuite provides a more general interface to, what is known as, external memory, although, as will be seen, the memory does not have to be external.

Like PMP access, the tool-chain needs to learn about external memories that are being attached. Unlike PMP access, however, the compiler does not know how to access these memories. A mechanism is provided by which an application can specify how such memories should be accessed.

Addresses of external objects are all 32 bits in size. The largest attachable memory is 64K (16 bits); the other 16 bits in the address is used to uniquely identify the memory. A total of 64K (16 bits) of these may be (theoretically) attached.

To use this feature, work through the following sections.