MAXQ610_11 Datasheet, PDF (12/29 Pages) Maxim Integrated Products – 16-Bit Microcontroller with Infrared Module 1.70V to 3.6V Operating Voltage Range

16-Bit Microcontroller with Infrared Module
Table 1. Memory Areas and Associated Maximum Privilege Levels
AREA
System
User Loader
User Application
Utility ROM
Other (RAM)
PAGE ADDRESS
0 to ULDR-1
ULDR to UAPP-1
UAPP to top
N/A
N/A
MAXIMUM PRIVILEGE LEVEL
High
Medium
Low
High
Low
Memory Protection
The optional memory-protection feature separates code
memory into three areas: system, user loader, and user
application. Code in the system area can be kept confi-
dential. Code in the user areas can be prevented from
reading and writing system code. The user loader can
also be protected from user application code.
Memory protection is implemented using privilege lev-
els for code. Each area has an associated privilege
level. RAM/ROM are assigned privilege levels as well.
Refer to the MAXQ610 User’s Guide for a more thor-
ough explanation of the topic. See Table 1.
Stack Memory
A 16-bit-wide internal stack provides storage for program
return addresses and can also be used general-purpose
data storage. The stack is used automatically by the
processor when the CALL, RET, and RETI instructions
are executed and when an interrupt is serviced. An
application can also store values in the stack explicitly by
using the PUSH, POP, and POPI instructions.
On reset, the stack pointer, SP, initializes to the top of
the stack (0Fh). The CALL, PUSH, and interrupt-vector-
ing operations increment SP, then store a value at the
location pointed to by SP. The RET, RETI, POP, and
POPI operations retrieve the value at SP and then
decrement SP.
Utility ROM
The utility ROM is a 5.25KB block of internal ROM mem-
ory that defaults to a starting address of 8000h. The util-
ity ROM consists of subroutines that can be called from
application software. These include the following:
• In-system programming (bootstrap loader) using
JTAG interface
• In-circuit debug routines
• Test routines (internal memory tests, memory loader,
etc.)
• User-callable routines for in-application flash pro-
gramming and fast table lookup
Following any reset, execution begins in the utility ROM.
The ROM software determines whether the program
execution should immediately jump to location 0000h,
the start of system code, or to one of the special rou-
tines mentioned. Routines within the utility ROM are
user accessible and can be called as subroutines by
the application software. More information on the utility
ROM functions is contained in the MAXQ610 User’s
Guide.
Some applications require protection against unautho-
rized viewing of program code memory. For these
applications, access to in-system programming, in-
application programming, or in-circuit debugging func-
tions is prohibited until a password has been supplied.
The password is defined as the 16 words of physical
program memory at addresses 0010h to 001Fh.
Three password locks are provided for protection of up
to three different program memory segments. When the
PWL is set to 1 (POR default) and the contents of the
memory at addresses 0010h to 001Fh are any value
other than FFh or 00h, the password is required to
access the utility ROM, including in-circuit debug and
in-system programming routines that allow reading or
writing of internal memory. When PWL is cleared to 0,
these utilities are fully accessible without password.
The password is automatically set to all ones following
a mass erase.
Watchdog Timer
An internal watchdog timer greatly increases system
reliability. The timer resets the device if software execu-
tion is disturbed. The watchdog timer is a free-running
counter designed to be periodically reset by the appli-
cation software. If software is operating correctly, the
counter is periodically reset and never reaches its max-
imum count. However, if software operation is interrupt-
ed, the timer does not reset, triggering a system reset
and optionally a watchdog timer interrupt. This protects
the system against electrical noise or ESD upsets that
could cause uncontrolled processor operation. The
internal watchdog timer is an upgrade to older designs
with external watchdog devices, reducing system cost
and simultaneously increasing reliability.
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