Datasheet

PIC16(L)F1938/9
DS40001574C-page 116  2011-2013 Microchip Technology Inc.
11.4 Modifying Flash Program Memory
When modifying existing data in a program memory
row, and data within that row must be preserved, it must
first be read and saved in a RAM image. Program
memory is modified using the following steps:
1. Load the starting address of the row to be mod-
ified.
2. Read the existing data from the row into a RAM
image.
3. Modify the RAM image to contain the new data
to be written into program memory.
4. Load the starting address of the row to be rewrit-
ten.
5. Erase the program memory row.
6. Load the write latches with data from the RAM
image.
7. Initiate a programming operation.
8. Repeat steps 6 and 7 as many times as required
to reprogram the erased row.
11.5 User ID, Device ID and
Configuration Word Access
Instead of accessing program memory or EEPROM
data memory, the User ID’s, Device ID/Revision ID and
Configuration Words can be accessed when CFGS = 1
in the EECON1 register. This is the region that would
be pointed to by PC<15> = 1, but not all addresses are
accessible. Different access may exist for reads and
writes. Refer to Table 11-2.
When read access is initiated on an address outside the
parameters listed in Table 11-2, the EEDATH:EEDATL
register pair is cleared.
TABLE 11-2: USER ID, DEVICE ID AND CONFIGURATION WORD ACCESS (CFGS = 1)
EXAMPLE 11-3: CONFIGURATION WORD AND DEVICE ID ACCESS
Address Function Read Access Write Access
8000h-8003h User IDs Yes Yes
8006h Device ID/Revision ID Yes No
8007h-8008h Configuration Words 1 and 2 Yes No
* This code block will read 1 word of program memory at the memory address:
* PROG_ADDR_LO (must be 00h-08h) data will be returned in the variables;
* PROG_DATA_HI, PROG_DATA_LO
BANKSEL EEADRL ; Select correct Bank
MOVLW PROG_ADDR_LO ;
MOVWF EEADRL ; Store LSB of address
CLRF EEADRH ; Clear MSB of address
BSF EECON1,CFGS ; Select Configuration Space
BCF INTCON,GIE ; Disable interrupts
BSF EECON1,RD ; Initiate read
NOP ; Executed (See Figure 11-1)
NOP ; Ignored (See Figure 11-1)
BSF INTCON,GIE ; Restore interrupts
MOVF EEDATL,W ; Get LSB of word
MOVWF PROG_DATA_LO ; Store in user location
MOVF EEDATH,W ; Get MSB of word
MOVWF PROG_DATA_HI ; Store in user location