PIC24FJ256GB110-I Datasheet, PDF (279/328 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

PIC24FJ256GB110 FAMILY
25.3.1 WINDOWED OPERATION
The Watchdog Timer has an optional fixed-window
mode of operation. In this Windowed mode, CLRWDT
instructions can only reset the WDT during the last 1/4
of the programmed WDT period. A CLRWDT instruction
executed before that window causes a WDT Reset,
similar to a WDT time-out.
Windowed WDT mode is enabled by programming the
WINDIS Configuration bit (CW1<6>) to ‘0’.
25.3.2 CONTROL REGISTER
The WDT is enabled or disabled by the FWDTEN
Configuration bit. When the FWDTEN Configuration bit
is set, the WDT is always enabled.
The WDT can be optionally controlled in software when
the FWDTEN Configuration bit has been programmed
to ‘0’. The WDT is enabled in software by setting the
SWDTEN control bit (RCON<5>). The SWDTEN
control bit is cleared on any device Reset. The software
WDT option allows the user to enable the WDT for
critical code segments and disable the WDT during
non-critical segments for maximum power savings.
FIGURE 25-2:
SWDTEN
FWDTEN
LPRC Input
All Device Resets
Transition to
New Clock Source
Exit Sleep or
Idle Mode
CLRWDT Instr.
PWRSAV Instr.
Sleep or Idle Mode
WDT BLOCK DIAGRAM
LPRC Control
FWPSA
31 kHz
Prescaler
(5-bit/7-bit)
WDT
Counter
1 ms/4 ms
WDTPS3:WDTPS0
Postscaler
1:1 to 1:32.768
Wake from Sleep
WDT Overflow
Reset
25.4 Program Verification and
Code Protection
PIC24FJ256GB110 family devices provide two compli-
mentary methods to protect application code from
overwrites and erasures. These also help to protect the
device from inadvertent configuration changes during
run time.
25.4.1 GENERAL SEGMENT PROTECTION
For all devices in the PIC24FJ256GB110 family, the
on-chip program memory space is treated as a single
block, known as the General Segment (GS). Code pro-
tection for this block is controlled by one Configuration
bit, GCP. This bit inhibits external reads and writes to
the program memory space. It has no direct effect in
normal execution mode.
Write protection is controlled by the GWRP bit in the
Configuration Word. When GWRP is programmed to
‘0’, internal write and erase operations to program
memory are blocked.
25.4.2 CODE SEGMENT PROTECTION
In addition to global General Segment protection, a
separate subrange of the program memory space can
be individually protected against writes and erases.
This area can be used for many purposes where a sep-
arate block of write and erase protected code is
needed, such as bootloader applications. Unlike
common boot block implementations, the specially
protected segment in PIC24FJ256GB110 family
devices can be located by the user anywhere in the
program space, and configured in a wide range of
sizes.
Code segment protection provides an added level of
protection to a designated area of program memory, by
disabling the NVM safety interlock whenever a write or
erase address falls within a specified range. They do
not override General Segment protection controlled by
the GCP or GWRP bits. For example, if GCP and
GWRP are enabled, enabling segmented code protec-
tion for the bottom half of program memory does not
undo General Segment protection for the top half.
© 2008 Microchip Technology Inc.
Preliminary
DS39897B-page 277