Rainbow Electronics MAXQ3120 - Manual (Page 12)

MAXQ3120
Following any reset, execution begins in the utility
ROM. The ROM software determines whether the pro-
gram execution should immediately jump to the start of
user-application code (located at address 0000h), or to
one of the special routines mentioned. Routines within
the utility ROM are user-accessible and can be called
as subroutines by the application software. More infor-
mation on the utility ROM contents is contained in the
user’s guide supplement for this device.
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.
A single password-lock (PWL) bit is implemented in the
SC register. When the PWL is set to one (power-on
reset default), 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 zero, these
utilities are fully accessible without the password. The
password is automatically set to all ones following a
mass erase.
Programming
The flash memory of the microcontroller can be pro-
grammed by two different methods: in-system program-
ming and in-application programming. Both methods
afford great flexibility in system design as well as reduce
the life-cycle cost of the embedded system. These fea-
tures can be password protected to prevent unautho-
rized access to code memory.
In-System Programming
An internal bootstrap loader allows the device to be
reloaded over a simple JTAG interface. As a result, sys-
tem software can be upgraded in-system, eliminating
the need for a costly hardware retrofit when software
updates are required. Remote software uploads are
possible that enable physically inaccessible applica-
tions to be frequently updated. The interface hardware
can be a JTAG connection to another microcontroller, or
a connection to a PC serial port using a serial-to-JTAG
converter such as the MAXQJTAG-001, available from
Maxim Integrated Products/Dallas Semiconductor. If in-
system programmability is not required, a commercial
gang programmer can be used for mass programming.
Activating the JTAG interface and loading the test
access port (TAP) with the system programming instruc-
tion invokes the bootloader. Setting the SPE bit to 1 dur-
ing reset through the JTAG interface executes the
bootloader-mode program that resides in the utility
ROM. When programming is complete, the bootloader
can clear the SPE bit and reset the device, allowing the
device to bypass the utility ROM and begin execution of
the application software.
The following bootloader functions are supported:
• Load
• Dump
• CRC
• Verify
• Erase
In-Application Programming
The in-application programming feature allows the
microcontroller to modify its own flash program memory
while simultaneously executing its application software.
This allows on-the-fly software updates in mission-criti-
cal applications that cannot afford downtime.
Alternatively, it allows the application to develop custom
loader software that can operate under the control of the
application software. The utility ROM contains user-
accessible flash programming functions that erase and
program flash memory. These functions are described
in detail in the user’s guide supplement for this device.
Register Set
Most functions of the device are controlled by sets of
registers. These registers provide a working space for
memory operations as well as configuring and address-
ing peripheral registers on the device. Registers are
divided into two major types: system registers and
peripheral registers. The common register set, also
known as the system registers, includes the ALU, accu-
mulator registers, data pointers, interrupt vectors and
control, and stack pointer. The peripheral registers
define additional functionality that may be included by
different products based on the MAXQ architecture.
This functionality is broken up into discrete modules so
that only the features required for a given product need
to be included. Tables 1 and 4 show the MAXQ3120
register set.
High-Precision ADC
Mixed-Signal Microcontroller
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