Maxim Integrated Secure Microcontroller - Manual (Page 18)

Secure Microcontroller User’s Guide
18 of 187
4. PROGRAMMER’S GUIDE
The secure microcontroller uses NV RAM technology for program and data memory. NV SRAM write-
protected memory segments are designated as program memory. The remaining RAM area is used as
nonvolatile data storage. One of the advantages of breaking a common RAM into two segments is that a
smaller number of memory chips is needed. For example, if a system requires 24kB of program memory
and 4kB of data memory, this all fits within one 32kB x 8 SRAM. The secure microcontroller can
subdivide this RAM into program and data segments, unconditionally write-protecting the program area.
The process of dividing the common memory space into ROM and RAM is called partitioning. The
original DS5000 series could partition one SRAM of up to 32kB. It could access a second RAM, but this
was restricted to data memory only. The DS5001/DS5002 series can partition two 32kB SRAMs, or even
one 128kB x 8 SRAM. Common elements of the programming model are detailed in the following
paragraphs, with individual differences highlighted.
4.1 Secure Microcontroller Memory Organization
Secure microcontrollers follow the standard 8051 convention of three memory areas. These include
internal registers, program memory, and data memory. These memory areas are not contiguous and are
accessed in different ways. The secure microcontroller duplicates all standard 8051 registers and adds
several new ones. They have a 64kB program and 64kB data space. However, secure microcontrollers
provide several ways to access these areas, and these features are what make the family unique.
Figure 4-1 shows the memory map of secure microcontrollers in general terms. The specific details and
access to the memory areas are discussed below.
Figure 4-1. Secure Microcontroller Memory Map
SCRATCH PAD
REGISTERS
SPECIAL
FUNCTION
REGISTERS
FFh
7Fh
00
FFFFh--
0000
PROGRAM
MEMORY
64kB
DATA
MEMORY
INTERNAL REGISTERS