5 Memory Organization
Like all 80C51 devices, the MPC82G516A has separate address spaces for program and data memory. The
logical separation of program and data memory allows the data memory to be accessed by 8-bit addresses,
which can be quickly stored and manipulated by the 8-bit CPU.
Program memory (ROM) can only be read, not written to. There can be up to 64k bytes of program memory. In
the MPC82G516A, all the program memory are on-chip Flash memory, and without the capability of accessing
external program memory because of no External Access Enable (/EA) and Program Store Enable (/PSEN)
signals designed.
Data memory occupies a separate address space from program memory. In the MPC82G516A, there are 256
bytes of internal scratch-pad RAM. Up to 64K bytes of memory space for external data memory. The CPU
generates the 16-bit addresses through the DPTR register and read and write strobe signals (/RD and /WR,
respectively) as needed during external data memory accesses. For many applications which need a little more
internal RAM, the MPC82G516A has incorporated 1024 bytes of external RAM to become on-chip expanded
RAM (called XRAM).
5.1 Program Memory
Program memory is the memory which stores the program codes for the CPU to execute, as shown in Figure 5-1.
After reset, the CPU begins execution from location 0000H, where should be the starting of the user’s application
code. To service the interrupts, the interrupt service locations (called interrupt vectors) should be located in the
program memory. Each interrupt is assigned a fixed location in the program memory. The interrupt causes the
CPU to jump to that location, where it commences execution of the service routine. External Interrupt 0, for
example, is assigned to location 0003H. If External Interrupt 0 is going to be used, its service routine must begin
at location 0003H. If the interrupt is not going to be used, its service location is available as general purpose
program memory.
The interrupt service locations are spaced at an interval of 8 bytes: 0003H for External Interrupt 0, 000BH for
Timer 0, 0013H for External Interrupt 1, 001BH for Timer 1, etc. If an interrupt service routine is short enough (as
is often the case in control applications), it can reside entirely within that 8-byte interval. Longer service routines
can use a jump instruction to skip over subsequent interrupt locations, if other interrupts are in use.
Note that, for the MPC82G516A, there is no capability of execution of external program. All the user’s program
code are programmed in the on-chip Flash memory. So, the /EA and /PSEN signals are no more needed and
thus omitted. The user should pay attention to it.
Figure 5-1. Program Memory
Program
Memory
FFFFH
001BH
0013H
Interrupt
8 Bytes
Locations
000BH
0003H
0000H
Reset
MEGAWIN
MPC82G516A Data Sheet
18
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