Introduction


All memory in the RPD-95 is organized as a series of eight-byte registers. These include data registers and system registers. Normally, system registers are protected and you can access only the data registers. By removing system protection, however, you can gain direct access to all registers.


The System-Protected Mode

Each time you turn on the calculator, the system is protected. In the system-protected mode, you can:
  • Access the 16 user flags (00-15) using the SF, RF, and TF instructions
  • Access data registers using functions such as STO, RCL, and DSZ followed by a three-digit register address.
  • Enter a program into the program memory by using the learn mode.
  • Store and retrieve files in the file space or in a Constant Memory™ cartridge using the file operations.

The System-Unprotected Mode

Besides the functions available in the system-protected mode, the system-unprotected mode lets you:
  • Access the system flags (16-99) using the SF, RF, and TF instructions. (refer to "System Flags" in Appendix C for a list of the system flags.)
  • Access data registers or system registers using functions such as STO, RCL, and DSZ followed by a four-digit register address.
  • Store or Recall a single byte in any user memory area, system register, or Constant Memory cartridge by using the STB and RCB instructions.
  • Call an assembly-language subroutine by using the SBA function.

Note:

You can use any of the system functions from the keyboard or from within a program. To store a system function as a program instruction, however, you must remove the system protection BEFORE entering the learn mode. In the Program Editor view, use the assembler directive SYS to remove protection in programs being edited/created.

Precaution for Using the Unprotected Mode

The procedure described in the next section shows you how to remove the system protection.

Unless you have a specific reason for accessing a system register, always leave the calculator in the protected mode. This prevents you from inadvertently changing any system registers that may affect the operation of the calculator.

Each system register has a fixed use that is determined by the design of the calculator. If you accidentally or indiscriminately change the contents of a system register, you could alter option settings or destroy important data.

In extreme cases, you could temporarily disable the display or keyboard. In such as case, you must press the RESET button to restore normal operation.


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