6 monitor rom, 7 random-access memory (ram), Monitor rom – Freescale Semiconductor MC68HC908MR32 User Manual

Page 37: Random-access memory (ram)

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Monitor ROM

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

Freescale Semiconductor

37

2.6 Monitor ROM

The 240 bytes at addresses $FE10–$FEFF are reserved ROM addresses that contain the instructions for
the monitor functions. See

18.3 Monitor ROM (MON)

.

2.7 Random-Access Memory (RAM)

Addresses $0060–$035F 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 160 bytes of RAM. Because the location of the stack RAM is programmable, all page
zero RAM locations can be used for input/output (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 central processor unit (CPU) uses five bytes of the stack to save the
contents of the CPU registers.

NOTE

For M68HC05 and M1468HC05 compatibility, the H register is not stacked.

$FFEE

PWMMC vector (high)

$FFEF

PWMMC vector (low)

$FFF0

FAULT 4 (high)

$FFF1

FAULT 4 (low)

$FFF2

FAULT 3 (high)

$FFF3

FAULT 3 (low)

$FFF4

FAULT 2 (high)

$FFF5

FAULT 2 (low)

$FFF6

FAULT 1 (high)

$FFF7

FAULT 1 (low)

$FFF8

PLL vector (high)

$FFF9

PLL vector (low)

$FFFA

IRQ vector (high)

$FFFB

IRQ vector (low)

$FFFC

SWI vector (high)

$FFFD

SWI vector (low)

High

$FFFE

Reset vector (high)

$FFFF

Reset vector (low)

Table 2-1. Vector Addresses (Continued)

Address

Vector

Priority

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