MAXQ2000-RFX+ datasheet(15/39 Pages) MAXIM

15 / 39 page

Low-Power LCD Microcontroller

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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.

Utility ROM

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

or UART interfaces

• 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 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.

Programming

The flash memory of the microcontroller can be pro-

grammed by two different methods: in-system pro-

gramming 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 features can be password protected to prevent

unauthorized 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,

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.

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