2 sram memory, 3 utility rom, 4 stack memory – Maxim Integrated MAX31782 User Manual
Page 9: 4 program and data memory mapping and access, 2 .4 program and data memory mapping and access -5
MaximIntegrated 2-5
MAX31782 User’s Guide
Revision 0; 8/11
2.3.2SRAMMemory
The MAX31782 contains 1KWords (1K x 16) of SRAM memory . The SRAM memory address begins at address 0000h
and is contiguous through word address 03FFh . The contents of the SRAM are indeterminate after power-on reset, but
are maintained during stop mode and non-POR resets .
When using the in-circuit debugging features, the highest 19 bytes of the SRAM must be reserved for saved state
storage and working space for the debugging routines . If in-circuit debug is not used, the entire 1KWords of SRAM is
available for application use .
2.3.3UtilityROM
The utility ROM is a 4KWord segment of memory . The utility ROM memory address begins at word address 8000h and
is contiguous through word address 8FFFh . The utility ROM is programmed at the factory and cannot be modified . The
utility ROM provides the following system utility functions:
• Reset vector (not user code reset vector)
• In-system programming (bootstrap loader) over JTAG or I
2
C-compatible interfaces
• In-circuit debug routines
• Routines for in-application flash programming
Following any reset, the MAX31782 automatically starts execution at the reset vector, which is address 8000h in the utility
ROM . The ROM code determines whether the program execution should immediately jump to the start of application code
(flash address 0000h), or to one of the special routines mentioned . Routines within the utility ROM are firmware-accessible
and can be called as subroutines by the application software . See
, and
SECTION 17: In-Circuit Debug Mode
for more information on the routines provided by the utility ROM .
2.3.4StackMemory
A 16-bit, 16-level on-chip stack provides storage for program return addresses and general-purpose use . The stack is
used automatically by the processor when the CALL, RET, and RETI instructions are executed, and when an interrupt is
serviced . The stack can also be used explicitly to store and retrieve data by using the @SP- - source, @++SP destina-
tion, or the PUSH, POP, and POPI instructions . The POPI instruction acts identically to the POP instruction except that
it additionally clears the INS bit .
The width of the stack is 16 bits to accommodate the instruction pointer size . On reset, the stack pointer SP initializes
to the top of the stack (0Fh) . The CALL, PUSH, and interrupt vectoring operations first increment SP and then store a
value at @SP . The RET, RETI, POP, and POPI operations first retrieve the value at @SP and then decrement SP .
The stack memory is initialized to indeterminate values upon reset or power-up . Stack memory is dedicated for stack
operations only and cannot be accessed by the MAX31782 program or data busses .
When using the in-circuit debugging features, one word of the stack must be reserved for the debugging routines . If
in-circuit debug is not used, the entire stack is available for application use .
2.4ProgramandDataMemoryMappingandAccess
The memory on the MAX31782 is implemented using a Harvard architecture, with separate buses for program and data
memory . The memory management unit (MMU) allows the MAX31782 to also support a pseudo-Von Neumann memory
map . The pseudo-Von Neumann memory map allows each of the memory segments (flash, SRAM, and utility ROM) to
be logically mapped into a single contiguous memory map . This allows all the memory segments to be accessed as
both program and memory data . The advantages the pseudo-Von Neumann memory map provides are:
• Program execution can occur from the flash, SRAM, or utility ROM memory segments .
• The SRAM and flash memory segments can both be used for data memory .
Using the pseudo-Von Neumann memory map does have one restriction . This restriction is that a particular memory
segment cannot be simultaneously accessed as both program and data memory .