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MAXQ610X-0000+ Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAXQ610X-0000+ Datasheet(HTML) 11 Page - Maxim Integrated Products |
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11 / 28 page  16-Bit Microcontroller with Infrared Module ______________________________________________________________________________________ 11 Memory Protection The optional memory-protection feature separates code memory into three areas: system, user loader, and user application. Code in the system area can be kept confi- dential. Code in the user areas can be prevented from reading and writing system code. The user loader can also be protected from user application code. Memory protection is implemented using privilege lev- els for code. Each area has an associated privilege level. RAM/ROM are assigned privilege levels as well. Refer to the MAXQ Family User's Guide: MAXQ610 Supplement for a more thorough explanation of the topic. See Table 1. Stack Memory A 16-bit-wide internal stack provides storage for program return addresses and can also be used general-purpose data storage. The stack is used automatically by the processor when the CALL, RET, and RETI instructions are executed and when an interrupt is serviced. An application can also store values in the stack explicitly 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-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 at SP and then decrement SP. Utility ROM The utility ROM is a 5.25KB block of internal ROM mem- ory that defaults to a starting address of 8000h. The util- ity ROM consists of subroutines that can be called from application software. These include the following: • In-system programming (bootstrap loader) using JTAG interface • 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 program execution should immediately jump to location 0000h, the start of system code, or to one of the special rou- tines mentioned. Routines within the utility ROM are user accessible and can be called as subroutines by the application software. More information on the utility ROM functions is contained in the MAXQ Family User’s Guide: MAXQ610 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 0010h to 001Fh. Three password locks are provided for protection of up to three different program memory segments. When the PWL is set to 1 (POR default) and the contents of the memory at addresses 0010h to 001Fh are any value other than FFh or 00h, the password is required to access the utility ROM, including in-circuit debug and in-system pro- gramming routines that allow reading or writing of internal memory. When PWL is cleared to 0, these utilities are fully accessible without password. The password is automatically set to all ones following a mass erase. Watchdog Timer An internal watchdog timer greatly increases system reliability. The timer resets the device if software execu- tion is disturbed. The watchdog timer is a free-running counter designed to be periodically reset by the appli- cation software. If software is operating correctly, the counter is periodically reset and never reaches its max- imum count. However, if software operation is interrupt- ed, the timer does not reset, triggering a system reset and optionally a watchdog timer interrupt. This protects the system against electrical noise or ESD upsets that could cause uncontrolled processor operation. The internal watchdog timer is an upgrade to older designs with external watchdog devices, reducing system cost and simultaneously increasing reliability. AREA PAGE ADDRESS MAXIMUM PRIVILEGE LEVEL System 0 to ULDR-1 High User Loader ULDR to UAPP-1 Medium User Application UAPP to top Low Utility ROM N/A High Other (RAM) N/A Low Table 1. Memory Areas and Associated Maximum Privilege Levels |
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