远程通信的实施

This application note discusses how to implement “long
calls” in the PIC16C5X architecture. The use of long call
can simplify the partitioning of the application program
with minimal software overhead.
In the PIC16C5X architecture, the program memory
page size is 512 words. Depending on the device, the
program memory may be as large as 2K words (as in
the PIC16C57 or PIC16C58 devices). The program
counter (and stack) width range from 9- to 11-bits,
depending on the amount of program memory. Table 1
shows the width of the Program Counter (PC) and
Stack for the various devices.
The low order 8-bits of the program counter are
accessible by the user program. These bits are
contained in the PC register.
AN581
Implementing Long Calls
Figure 1 shows the structure of the PC. Since A8 is
Author: Mark Palmer forced to 0 by CALL instructions, the start address of
Microchip Technology Inc. subroutines must be in the rst 256 words of each pro-
gram memory page. Depending on the size and num-
ber of called subroutines, this limitation may become a
INTRODUCTION