Freescale Semiconductor, Inc.
GENERAL RELEASE SPECIFICATION
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SECTION 2
MEMORY
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2.1 Introduction
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The MC68HC805P18 utilizes 14 address lines to access an internal memory space
covering 16 Kbytes. This memory space is divided into I/O, RAM, EEPROM, and
boot ROM areas.
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2.2 User Mode Memory Map
When the MC68HC805P18 is in the user mode, the 32 bytes of I/O, 192 bytes of
RAM, 128 bytes of EEPROM, 8000 bytes of program EEPROM, 48 bytes of user
page zero EEPROM, and 16 bytes of user vectors EEPROM are all active as
shown in Figure 2-1.
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2.3 I/O and Control Registers
Figure 2-2 through Figure 2-4 briefly describe the I/O and control registers at
locations $0000–$001F. Reading unimplemented bits will return unknown states,
and writing unimplemented bits will be ignored.
2.4 RAM
The user RAM consists of 192 bytes (including the stack) at locations $0050
through $010F. The stack begins at address $00FF. The stack pointer can access
64 bytes of RAM from $00FF to $00C0.
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NOTE
Using the stack area for data storage or temporary work locations
requires care to prevent it from being overwritten due to stacking
from an interrupt or subroutine call.
MEMORY
Rev. 1.0
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