XC164CS
Derivatives
Functional Description
Data Sheet 18 V2.3, 2006-08
3.1 Memory Subsystem and Organization
The memory space of the XC164CS is configured in a Von Neumann architecture, which
means that all internal and external resources, such as code memory, data memory,
registers and I/O ports, are organized within the same linear address space. This
common memory space includes 16 Mbytes and is arranged as 256 segments of
64 Kbytes each, where each segment consists of four data pages of 16 Kbytes each.
The entire memory space can be accessed bytewise or wordwise. Portions of the on-
chip DPRAM and the register spaces (E/SFR) have additionally been made directly
bitaddressable.
The internal data memory areas and the Special Function Register areas (SFR and
ESFR) are mapped into segment 0, the system segment.
The Program Management Unit (PMU) handles all code fetches and, therefore, controls
accesses to the program memories, such as Flash memory, ROM, and PSRAM.
The Data Management Unit (DMU) handles all data transfers and, therefore, controls
accesses to the DSRAM and the on-chip peripherals.
Both units (PMU and DMU) are connected via the high-speed system bus to exchange
data. This is required if operands are read from program memory, code or data is written
to the PSRAM, code is fetched from external memory, or data is read from or written to
external resources, including peripherals on the LXBus (such as TwinCAN). The system
bus allows concurrent two-way communication for maximum transfer performance.
64/128 Kbytes1) of on-chip Flash memory or mask-programmable ROM store code
or constant data. The on-chip Flash memory is organized as four 8-Kbyte sectors, one
32-Kbyte sector, and one 64-Kbyte sector. Each sector can be separately write
protected2), erased and programmed (in blocks of 128 Bytes). The complete Flash or
ROM area can be read-protected. A password sequence temporarily unlocks protected
areas. The Flash module combines very fast 64-bit one-cycle read accesses with
protected and efficient writing algorithms for programming and erasing. Thus, program
execution out of the internal Flash results in maximum performance. Dynamic error
correction provides extremely high read data security for all read accesses.
For timing characteristics, please refer to Section 4.4.2.
2 Kbytes of on-chip Program SRAM (PSRAM) are provided to store user code or data.
The PSRAM is accessed via the PMU and is therefore optimized for code fetches.
2/4 Kbytes1) of on-chip Data SRAM (DSRAM) are provided as a storage for general
user data. The DSRAM is accessed via the DMU and is therefore optimized for data
accesses.
2 Kbytes of on-chip Dual-Port RAM (DPRAM) are provided as a storage for user
defined variables, for the system stack, and general purpose register banks. A register
1) Depends on the respective derivative. The derivatives are listed in Table 1.
2) Each two 8-Kbyte sectors are combined for write-protection purposes.