MC68HC908GR16 Datasheet, PDF (38/310 Pages) Motorola, Inc – Microcontrollers

Memory
Freescale Semiconductor, Inc.
2.5 Random-Access Memory (RAM)
Addresses $0040 through $043F are RAM locations. The location of the stack
RAM is programmable. The 16-bit stack pointer allows the stack to be anywhere in
the 64-Kbyte memory space.
NOTE: For correct operation, the stack pointer must point only to RAM locations.
Within page zero are 192 bytes of RAM. Because the location of the stack RAM is
programmable, all page zero RAM locations can be used for I/O control and user
data or code. When the stack pointer is moved from its reset location at $00FF out
of page zero, direct addressing mode instructions can efficiently access all page
zero RAM locations. Page zero RAM, therefore, provides ideal locations for
frequently accessed global variables.
Before processing an interrupt, the CPU uses five bytes of the stack to save the
contents of the CPU registers.
NOTE: For M6805 compatibility, the H register is not stacked.
During a subroutine call, the CPU uses two bytes of the stack to store the return
address. The stack pointer decrements during pushes and increments during pulls.
NOTE: Be careful when using nested subroutines. The CPU may overwrite data in the
RAM during a subroutine or during the interrupt stacking operation.
2.6 FLASH Memory (FLASH)
This subsection describes the operation of the embedded FLASH memory. This
memory can be read, programmed, and erased from a single external supply. The
program, erase, and read operations are enabled through the use of an internal
charge pump. It is recommended that the user utilize the FLASH programming
routines provided in the on-chip ROM, which are described more fully in a separate
Motorola application note.
2.6.1 Functional Description
The FLASH memory is an array of 15,872 bytes with an additional 44 bytes of user
vectors and one byte of block protection. An erased bit reads as logic 1 and a
programmed bit reads as a logic 0. Memory in the FLASH array is organized into
two rows per page basis. For the 16-K word by 8-bit embedded FLASH memory,
the page size is 64 bytes per page and the row size is 32 bytes per row. Hence the
minimum erase page size is 64 bytes and the minimum program row size is 32
bytes. Program and erase operation operations are facilitated through control bits
in FLASH control register (FLCR). Details for these operations appear later in this
section.
Data Sheet
38
Memory
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MC68HC908GR16 — Rev. 1.0
MOTOROLA