DS2790 Maxim Integrated Products, DS2790 Datasheet - Page 11

• Manufacturer Part Number: DS2790
• Description: Programmable 1-Cell Li-Ion Fuel Gauge and Protector
• Manufacturer: Maxim Integrated Products

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Stack Memory
A 16-bit, 16-level internal stack provides storage for program 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. The stack can also be used explicitly to store and retrieve data 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-vectoring
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 4k word 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:
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 application code, or to one of the special routines
mentioned. Routines within the utility ROM are firmware-accessible and can be called as subroutines by the
application software. More information on the utility ROM contents is contained in the MAXQ Family User's Guide:
DS2790 Supplement.
Some applications require protection against unauthorized viewing of program code memory. For these
applications, access to in-system programming, in-application programming, or in-circuit debugging functions 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. Upon startup, code in the ROM examines the password, if a password is
defined (password is other than all zero’s or all one’s), the PWL bit remains set, which prohibits access to
commands to read memory contents over the JTAG and 2-wire interfaces.
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 EEPROM memory of the microcontroller can be programmed by two different methods: 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. 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 programmed over the JTAG or 2-wire interfaces. As a result,
system 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 applications to be
frequently updated. The JTAG 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. The 2-wire interface hardware can be an I
connection to a PC USB port using a USB to I
Semiconductor. A commercial gang programmer can also be used for programming.
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In-system programming (bootstrap loader) over JTAG or 2-wire interfaces
In-circuit debug routines
Internal self-test routines
callable routines for in-application EEPROM programming and SHA-1 calculations
DS2790 Programmable 1-Cell Li-Ion Fuel Gauge and Protector
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C converter such as the DS9123O, available from Dallas
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C connection to another microcontroller, or a