MAXQ7667AACM/V+T【PDF 21/40 页】IC MCU-BASED DAS 16BIT 48-LQFP

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MAXQ7667

16-Bit, RISC, Microcontroller-Based,

Ultrasonic Distance-Measuring System

______________________________________________________________________________________

memory. Access physical memory segments (other

than the stack and register memories) as either pro-

gram memory or data memory, but not both at once.

By default, the memory is arranged in a Harvard archi-

tecture, with separate address spaces for program and

data memory. The configuration of program and data

space depends on the current execution location.

When executing code from flash memory, access

the SRAM and utility ROM in data space.

When executing code from SRAM, access the

flash memory and utility ROM in data space.

When executing code from the utility ROM, access

the flash memory and SRAM in data space.

Utility ROM (see Section 18 of

the MAXQ7667 User’s Guide)

The utility ROM is a 4K x 16 block of internal ROM

memory that defaults to a starting address of 8000h.

The utility ROM consists of subroutines called from

application software. The subroutines include:

In-system programming (bootloader) over the

JTAG or UART interface

In-circuit debug routines

Test routines (internal memory tests, memory

loader, etc.)

User-callable routines for in-application flash pro-

gramming and code space table lookup

Following any reset, execution begins in the utility ROM.

The ROM software determines whether the program

execution immediately jumps to the start of the user-

application code (located at address 0000h) or to one

of the special routines mentioned above. Call the rou-

tines within the utility ROM using the application soft-

ware. Refer to the

MAXQ7667 User’s Guide for more

information on the utility ROM contents.

Password protect in-system programming, in-applica-

tion programming, and in-circuit debugging functions

using a password-lock (PWL) bit. The PWL bit is imple-

mented in the SC register. When the PWL bit is set to

one (POR default), the password is required to access

the utility ROM, including in-circuit debug and in-sys-

tem programming routines that allow reading or writing

of internal memory. When the PWL bit is cleared to

zero, these utilities are fully accessible without the

password. The password is automatically set to all ones

following a mass erase.

Data Memory

The 2K x 16 internal data SRAM maps into either pro-

gram or data space. The contents of the SRAM are

maintained during stop mode and across non-POR

resets, as long as DVDD remains within the operating

voltage range.

A data memory cycle requires only one system clock

period to support fast internal execution. This allows a

complete read or write operation on SRAM in one clock

cycle. The MMU handles data memory mapping and

access control. Read or write to the data memory with

word or byte-wide commands.

Stack Memory

The MAXQ7667 provides a 16 x 16 hardware stack to

support subroutine calls and system interrupts. A 16-bit

wide internal hardware stack provides storage for pro-

gram return addresses and general-purpose use. The

stack is used automatically by the processor when the

CALL, RET, and RETI instructions are executed and

interrupts serviced.

Sets of registers control most functions. These registers

provide a working space for memory operations as well

as configuring and addressing peripheral registers on

the device. Registers are divided into two major types;

system registers and peripheral registers. The register

set common to most MAXQ-based devices, also known

as the system registers, includes the ALU, accumulator

registers, data pointers, interrupt vectors and control,

and stack pointer. The peripheral registers define addi-

tional functionality. Tables 1 and 3 show the MAXQ7667

Programming

Two different methods program the flash memory: in-

system programming and in-application programming.

Both methods afford great flexibility in system design

as well as reduce the life-cycle cost of the embedded

system. The MAXQ7667 password protects these fea-

tures to prevent unauthorized access to code memory.

In-System Programming

An internal bootstrap loader reloads the device over a

simple JTAG or UART interface allowing cost savings in

system software upgrade. During power-up, the

MAXQ7667 first checks for activity on the JTAG port. If

no activity is present, the device checks if a password-

protected program is present. If the password is set,

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