mc908jl16 Freescale Semiconductor, Inc, mc908jl16 Datasheet - Page 33

• Manufacturer Part Number: mc908jl16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

2.4 Random-Access Memory (RAM)
Addresses $0060 through $025F 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.
Within page zero are 160 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 $00FF, direct addressing mode instructions can access efficiently all page zero
RAM locations. Page zero RAM, therefore, provides ideal locations for frequently accessed global
variables.
Before processing an interrupt, the CPU uses five bytes of the stack to save the contents of the CPU
registers.
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack
pointer decrements during pushes and increments during pulls.
2.5 FLASH Memory
This sub-section describes the operation of the embedded FLASH memory. The FLASH memory can be
read, programmed, and erased from a single external supply. The program and erase operations are
enabled through the use of an internal charge pump.
2.5.1 Functional Description
The FLASH memory consists of an array of 16,384 bytes for user memory plus a block of 36 bytes for
user interrupt vectors. An erased bit reads as 1 and a programmed bit reads as a 0. The FLASH memory
page size is defined as 64 bytes, and is the minimum size that can be erased in a page erase operation.
Program and erase operations are facilitated through control bits in FLASH control register (FLCR). The
address ranges for the FLASH memory are:
Programming tools are available from Freescale Semiconductor. Contact your local representative for
more information.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
Freescale Semiconductor
unauthorized users.
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$BC00–$FBFF; user memory; 16,384 bytes
$FFDC–$FFFF; user interrupt vectors; 36 bytes
For correct operation, the stack pointer must point only to RAM locations.
For M6805 compatibility, the H register is not stacked.
Be careful when using nested subroutines. The CPU may overwrite data in
the RAM during a subroutine or during the interrupt stacking operation.
A security feature prevents viewing of the FLASH contents.
MC68HC908JL16 Data Sheet, Rev. 1.1
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Random-Access Memory (RAM)
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