cop87l88rb National Semiconductor Corporation, cop87l88rb Datasheet - Page 60

• Manufacturer Part Number: cop87l88rb
• Description: 8-bit Cmos Otp Microcontrollers With 16k Or 32k Memory, Can Interface, 8-bit A/d, And Usart
• Manufacturer: National Semiconductor Corporation

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WATCHDOG Operation
WATCHDOG AND CLOCK MONITOR SUMMARY
The following salient points regarding the COP888 WATCH-
DOG and CLOCK MONITOR should be noted:
• Both the WATCHDOG and Clock Monitor detector cir-
• Following RESET, the WATCHDOG and CLOCK MONI-
• The WATCHDOG service window and Clock Monitor
• The initial WATCHDOG service must match the key data
• Subsequent WATCHDOG services must match all three
• The correct key data value cannot be read from the
• The WATCHDOG detector circuit is inhibited during both
• The Clock Monitor detector circuit is active during both
• With the single-pin R/C oscillator mask option selected
cuits are inhibited during RESET.
TOR are both enabled, with the WATCHDOG having the
maximum service window selected.
enable/disable option can only be changed once, during
the initial WATCHDOG service following RESET.
value in the WATCHDOG Service register WDSVR in or-
der to avoid a WATCHDOG error.
data fields in WDSVR in order to avoid WATCHDOG er-
rors.
WATCHDOG Service register WDSVR. Any attempt to
read this key data value of 01100 from WDSVR will read
as key data value of all 0’s.
the HALT and IDLE modes.
the HALT and IDLE modes. Consequently, the device in-
advertently entering the HALT mode will be detected as a
Clock Monitor error (provided that the Clock Monitor en-
able option has been selected by the program).
and the CLKDLY bit reset, the WATCHDOG service win-
dow will resume following HALT mode from where it left
off before entering the HALT mode.
Match
Don’t Care
Mismatch
Don’t Care
Data
Key
Match
Mismatch
Don’t Care
Don’t Care
Window
Data
(Continued)
TABLE 19. WATCHDOG Service Actions
Match
Don’t Care
Don’t Care
Mismatch
Monitor
Clock
60
• With the crystal oscillator mask option selected, or with
• The IDLE timer T0 is not initialized with RESET.
• The user can sync in to the IDLE counter cycle with an
• A hardware WATCHDOG service occurs just as the de-
• Following RESET, the initial WATCHDOG service (where
Valid Service: Restart Service Window
Error: Generate WATCHDOG Output
Error: Generate WATCHDOG Output
Error: Generate WATCHDOG Output
the single-pin R/C oscillator mask option selected and the
CLKDLY bit set, the WATCHDOG service window will be
set to its selected value from WDSVR following HALT.
Consequently, the WATCHDOG should not be serviced
for at least 2048 instruction cycles following HALT, but
must be serviced within the selected window to avoid a
WATCHDOG error.
IDLE counter (T0) interrupt or by monitoring the T0PND
flag. The T0PND flag is set whenever the thirteenth bit of
the IDLE counter toggles (every 4096 instruction cycles).
The user is responsible for resetting the T0PND flag.
vice exits the IDLE mode. Consequently, the WATCH-
DOG should not be serviced for at least 2048 instruction
cycles following IDLE, but must be serviced within the se-
lected window to avoid a WATCHDOG error.
the service window and the CLOCK MONITOR enable/
disable must be selected) may be programmed any-
where within the maximum service window (65,536 in-
struction cycles) initialized by RESET. Note that this initial
WATCHDOG service may be programmed within the inti-
tial 2048 instruction cycles without causing a WATCH-
DOG error.
Action