MAXQ2000 Maxim, MAXQ2000 Datasheet - Page 15

• Manufacturer Part Number: MAXQ2000
• Description: The MAXQ2000 microcontroller is a low-power, 16-bit device that incorporates a liquid-crystal display (LCD) interface that can drive up to 100 (-RBX/-RBX+) or 132 (-RAX/-RAX+/-RFX/-RFX+) segments
• Manufacturer: Maxim

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 @SP and then
decrement SP.
The utility ROM is a 4kB block of internal ROM memory
that defaults to a starting address of 8000h. The utility
ROM consists of subroutines that can be called from
application software. These include:
• In-system programming (bootstrap loader) over JTAG
• In-circuit debug routines
• Test routines (internal memory tests, memory
• User-callable routines for in-application flash pro-
Following any reset, execution begins in the utility
ROM. The ROM software determines whether the pro-
gram execution should immediately jump to location
0000h, the start of user-application code, or to one of
the special routines mentioned. Routines within the utili-
ty ROM are user-accessible and can be called as sub-
routines by the application software. More information
on the utility ROM contents is contained in the MAXQ
Family User’s Guide: MAXQ2000 Supplement .
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 x0010h to x001Fh.
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 password. The
password is automatically set to all ones following a
mass erase.
The flash memory of the microcontroller can be pro-
grammed by two different methods: in-system pro-
gramming and in-application programming. Both
or UART interfaces
loader, etc.)
gramming and fast table lookup
____________________________________________________________________
Programming
Low-Power LCD Microcontroller
Utility ROM
methods afford great flexibility in system design as well
as reduce the life-cycle cost of the embedded system.
These features can be password protected to prevent
unauthorized access to code memory.
An internal bootstrap loader allows the device to be
reloaded over a simple JTAG interface. As a result,
software can be upgraded in-system, eliminating the
need for a costly hardware retrofit when updates are
required. Remote software uploads are possible that
enable physically inaccessible applications to be fre-
quently updated. The interface hardware can be a
JTAG connection to another microcontroller, or a con-
nection to a PC serial port using a serial-to-JTAG con-
verter such as the MAXQJTAG-001, available from
Maxim Integrated Products. If in-system programmabili-
ty 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 bootstrap loader. Setting the SPE bit to
1 during reset through the JTAG interface executes the
bootstrap-loader-mode program that resides in the utility
ROM. When programming is complete, the bootstrap
loader can clear the SPE bit and reset the device, allow-
ing the device to bypass the utility ROM and begin exe-
cution of the application software.
The following bootstrap loader functions are supported:
• Load
• Dump
• CRC
• Verify
• Erase
Optionally, the bootstrap loader can be invoked by the
application code. In this mode, the application software
would configure the SPE and PSS bits for UART com-
munication, then jump to the start of the utility ROM. In
this way, the bootstrap loader can be accessed through
another UART-enabled peripheral, or a PC serial port
through an RS-232 transceiver such as the MAX232.
Because the bootstrap loader defaults to the JTAG con-
figuration on reset, the UART versus JTAG selection
must be made from the application code. As a result,
bootstrap loader access through the UART is not possi-
ble in an unprogrammed device.
In-System Programming
15