NVM - Nonvolatile Memory Control

The Nonvolatile Memory (NVM) module provides run-time read and write access to the Program Flash Memory (PFM), Data Flash Memory (DFM), and Configuration bits. PFM includes the program memory and user ID space. DFM is also referred to as EEPROM which is accessed one byte at a time and the erase before write is automatic.

NVM is accessible using both FSR and INDF registers, or through the NVMREG register interface (see Table 1).

The write time is controlled by an on-chip timer. The write/erase voltages are generated by an on-chip charge pump rated to operate over the operating voltage range of the device.

PFM and DFM can be protected in two ways: code protection and write protection. Code protection (Configuration bits CP (PFM)/CPD (DFM)) disables PFM/DFM read and write access through an external device programmer. Write protection prevents user software writes to NVM areas tagged for protection by the WRTn Configuration bits. Code protection does not affect the self-write and erase functionality, whereas write protection does. Attempts to write a protected location will set the WRERR bit. Code protection and write protection can only be reset on a Bulk Erase performed by an external programmer.

The Bulk Erase command is used to completely erase program memory. The Bulk Erase command can only be issued through an external programmer. There is no run time access for this command.

If the device is code-protected and a Bulk Erase command for the configuration memory is issued; all other memory regions are also erased. Refer to the ”Programming Specifications” document for more details.

Table 1. NVM Organization and Access Information
Main Values NVMREG Access FSR Access
Memory Function Memory Type Program Counter (PC), ICSP™ Address NVMREGS bit (NVMCON1) NVMADR[14:0] Allowed Operations FSR Address FSR Programming Access
Reset Vector Program Flash Memory 0x0000 0 0x0000 Read/Write 0x8000 Read-Only
User Memory 0x0001 0 0x0001 0x8001
0x0003 0x0003 0x8003
INT Vector 0x0004 0 0x0004 0x8004
User Memory 0x0005 0 0x0005 0x8005
0x3FFF(1) 0x3FFF(1) 0xFFFF
User ID Program Flash Memory 0x8000 1 0x0000 Read/Write No Access
0x8003 0x0003
Reserved 0x0004
Revision ID Hard Coded in Program Flash Memory 0x8005 1 0x0005 Read
Device ID 0x8006 1 0x0006
CONFIG1 Program Flash Memory 0x8007 1 0x0007 Read/Write
CONFIG2 0x8008 1 0x0008
CONFIG3 0x8009 1 0x0009
CONFIG4 0x800A 1 0x000A
CONFIG5 0x800B 1 0x000B
DIA and DCI Hard Coded in Program Flash Memory 0x8100 1 0x0100 Read
0x82FF 1 0x02FF
EEPROM Data Flash Memory 0xF000 1 0x7000 Read/Write 0x7000 Read
0xF0FF 0x70FF 0x70FF
Note:
  1. 1.The maximum Program Flash Memory address for the PIC16F171 family is 0x3FFF.