MC68HC705C9A Datasheet, PDF (25/118 Pages) Motorola, Inc – Microcontrollers

Chapter 2
Memory
2.1 Introduction
The MCU has a 16-Kbyte memory map when configured as either an MC68HC05C9A or an
MC68HC05C12A. The memory map consists of registers (I/O, control, and status), user RAM, user
EPROM, bootloader ROM, and reset and interrupt vectors as shown in Figure 2-1 and Figure 2-2.
When configured as an MC68HC05C9A, two control bits in the option register ($3FDF) allow the user to
switch between RAM and EPROM at any time in two special areas of the memory map, $0020-$004F (48
bytes) and $0100-$017F (128 bytes). When configured as an MC68HC05C12A, the section of the
memory map from $0020 to $004F is fixed as EPROM and the section from $0100 to $0FFF becomes
unused.
2.2 RAM
The main user RAM consists of 176 bytes at $0050–$00FF. This RAM area is always present in the
memory map and includes a 64-byte stack area. The stack pointer can access 64 bytes of RAM in the
range $00FF down to $00C0.
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.
In MC68HC05C9A configuration, two additional RAM areas are available at $0020–$004F (48 bytes) and
$0100–$017F (128 bytes) (see Figure 2-1 and Figure 2-2.) These may be accessed at any time by setting
the RAM0 and RAM1 bits, respectively, in the C9A option register. Refer to 1.5 Software-Programmable
Options (MC68HC05C9A Mode Only) for additional information.
2.3 EPROM
When configured as a C12A the main user EPROM consists of 48 bytes of page zero EPROM from $0020
to $004F, 12,032 bytes of EPROM from $1000 to $3EFF, and 14 bytes of user vectors from $3FF4 to
$3FFF. When configured as a C9A, an additional 3,840 bytes of user EPROM from $0100 to $0FFF are
enabled.
Locations $3FF0 and $3FF1 are the mask option registers (MOR) (see 1.4 Mask Options).
For detailed information on programming the EPROM see Appendix A EPROM Programming.
MC68HC05C9A Advance Information Data Sheet, Rev. 4.1
Freescale Semiconductor
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