2000 Microchip Technology Inc.
DS30605C-page 95
PIC16C63A/65B/73B/74B
13.6
Context Saving During Interrupts
During an interrupt, only the return PC value is saved
on the stack. Users may wish to save key registers dur-
ing an interrupt i.e., W register and STATUS register.
This will have to be implemented in software.
Example 13-1 stores and restores the STATUS, W, and
PCLATH registers. The register W_TEMP must be
defined in each bank and must be defined at the same
offset from the bank base address (i.e., if W_TEMP is
defined at 0x20 in bank 0, it must also be defined at
0xA0 in bank 1).
The example:
a)
Stores the W register.
b)
Stores the STATUS register in bank 0.
c)
Stores the PCLATH register.
d)
Executes the ISR code.
e)
Restores the STATUS register
(and bank select bit).
f)
Restores the W and PCLATH registers.
EXAMPLE 13-1:
SAVING STATUS, W, AND PCLATH REGISTERS IN RAM
MOVWF
W_TEMP
;Copy W to TEMP register, could be bank one or zero
SWAPF
STATUS,W
;Swap status to be saved into W
CLRF
STATUS
;bank 0, regardless of current bank, Clears IRP,RP1,RP0
MOVWF
STATUS_TEMP
;Save status to bank zero STATUS_TEMP register
MOVF
PCLATH, W
;Only required if using pages 1, 2 and/or 3
MOVWF
PCLATH_TEMP
;Save PCLATH into W
:
(ISR) ;User ISR code goes here
:
MOVF
PCLATH_TEMP, W
;Restore PCLATH
MOVWF
PCLATH
;Move W into PCLATH
SWAPF
STATUS_TEMP, W
;Swap STATUS_TEMP register into W
;(sets bank to original state)
MOVWF
STATUS
;Move W into STATUS register
SWAPF
W_TEMP,F
;Swap W_TEMP
SWAPF
W_TEMP,W
;Swap W_TEMP into W
13.7
Watchdog Timer (WDT)
The Watchdog Timer is a free running on-chip RC oscil-
lator, which does not require any external components.
This RC oscillator is separate from the RC oscillator of
the OSC1/CLKIN pin. The WDT will run, even if the
clock on the OSC1/CLKIN and OSC2/CLKOUT pins of
the device has been stopped, for example, by execu-
tion of a
SLEEP
instruction.
During normal operation, a WDT time-out generates a
device RESET (Watchdog Timer Reset). If the device is
in SLEEP mode, a WDT time-out causes the device to
wake-up and resume normal operation (Watchdog
Timer Wake-up).
The WDT can be permanently disabled by clearing
configuration bit WDTE (Section 13.1).
13.7.1
WDT PERIOD
The WDT has a nominal time-out period of 18 ms
(parameter #31, T
WDT
). The time-out periods vary with
temperature, V
DD
, and process variations. If longer
time-out periods are desired, a prescaler with a division
ratio of up to 1:128 can be assigned to the WDT under
software control, by writing to the OPTION register.
Time-out periods up to 128 T
WDT
can be realized.
The
CLRWDT
and
SLEEP
instructions clear the WDT
and the postscaler, if assigned to the WDT. In addition,
the
SLEEP
instruction prevents the WDT from generat-
ing a RESET, but will allow the WDT to wake the device
from SLEEP mode.
The TO bit in the STATUS register will be cleared upon
a WDT time-out.
Summary of Contents for PIC16C63A
Page 4: ...PIC16C63A 65B 73B 74B DS30605C page 4 2000 Microchip Technology Inc NOTES ...
Page 6: ...PIC16C63A 65B 73B 74B DS30605C page 6 2000 Microchip Technology Inc NOTES ...
Page 8: ...PIC16C63A 65B 73B 74B DS30605C page 8 2000 Microchip Technology Inc NOTES ...
Page 28: ...PIC16C63A 65B 73B 74B DS30605C page 28 2000 Microchip Technology Inc NOTES ...
Page 42: ...PIC16C63A 65B 73B 74B DS30605C page 42 2000 Microchip Technology Inc NOTES ...
Page 78: ...PIC16C63A 65B 73B 74B DS30605C page 78 2000 Microchip Technology Inc NOTES ...
Page 112: ...PIC16C63A 65B 73B 74B DS30605C page 112 2000 Microchip Technology Inc NOTES ...
Page 152: ...PIC16C63A 65B 73B 74B DS30605C page 152 2000 Microchip Technology Inc NOTES ...
Page 164: ...PIC16C63A 65B 73B 74B DS30605C page 164 2000 Microchip Technology Inc NOTES ...
Page 174: ...PIC16C63A 65B 73B 74B DS30605C page 174 2000 Microchip Technology Inc NOTES ...
Page 178: ...PIC16C63A 65B 73B 74B DS30605C page 178 2000 Microchip Technology Inc NOTES ...
Page 179: ... 2000 Microchip Technology Inc DS30605C page 179 PIC16C63A 65B 73B 74B NOTES ...
Page 180: ...PIC16C63A 65B 73B 74B DS30605C page 180 2000 Microchip Technology Inc NOTES ...
Page 181: ... 2000 Microchip Technology Inc DS30605C page 181 PIC16C63A 65B 73B 74B NOTES ...
Page 182: ...PIC16C63A 65B 73B 74B DS30605C page 182 2000 Microchip Technology Inc NOTES ...
Page 183: ... 2000 Microchip Technology Inc DS30605C page 183 PIC16C63A 65B 73B 74B NOTES ...