Datasheet
dsPIC33EPXXXGM3XX/6XX/7XX
DS70000689D-page 230 2013-2014 Microchip Technology Inc.
16.1.2 WRITE-PROTECTED REGISTERS
On dsPIC33EPXXXGM3XX/6XX/7XX devices, write
protection is implemented for the IOCONx and
FCLCONx registers. The write protection feature
prevents any inadvertent writes to these registers. This
protection feature can be controlled by the PWMLOCK
Configuration bit (FOSCSEL<6>). The default state of
the write protection feature is enabled (PWMLOCK = 1).
The write protection feature can be disabled by
configuring: PWMLOCK = 0.
To gain write access to these locked registers, the user
application must write two consecutive values of
0xABCD and 0x4321 to the PWMKEY register to
perform the unlock operation. The write access to the
IOCONx or FCLCONx registers must be the next SFR
access following the unlock process. There can be no
other SFR accesses during the unlock process and
subsequent write access. To write to both the IOCONx
and FCLCONx registers requires two unlock operations.
The correct unlocking sequence is described in
Example 16-1.
EXAMPLE 16-1: PWM1 WRITE-PROTECTED REGISTER UNLOCK SEQUENCE
; FLT32 pin must be pulled high externally in order to clear and disable the fault
; Writing to FCLCON1 register requires unlock sequence
mov #0xabcd, w10 ; Load first unlock key to w10 register
mov #0x4321, w11 ; Load second unlock key to w11 register
mov #0x0000, w0 ; Load desired value of FCLCON1 register in w0
mov w10, PWMKEY ; Write first unlock key to PWMKEY register
mov w11, PWMKEY ; Write second unlock key to PWMKEY register
mov w0, FCLCON1 ; Write desired value to FCLCON1 register
; Set PWM ownership and polarity using the IOCON1 register
; Writing to IOCON1 register requires unlock sequence
mov #0xabcd, w10 ; Load first unlock key to w10 register
mov #0x4321, w11 ; Load second unlock key to w11 register
mov #0xF000, w0 ; Load desired value of IOCON1 register in w0
mov w10, PWMKEY ; Write first unlock key to PWMKEY register
mov w11, PWMKEY ; Write second unlock key to PWMKEY register
mov w0, IOCON1 ; Write desired value to IOCON1 register