Datasheet

© 2009 Microchip Technology Inc. DS39663F-page 189
PIC18F87J10 FAMILY
18.4.7.1 Auto-Shutdown and Automatic
Restart
The auto-shutdown feature can be configured to allow
automatic restarts of the module following a shutdown
event. This is enabled by setting the P1RSEN bit of the
ECCP1DEL register (ECCP1DEL<7>).
In Shutdown mode with P1RSEN = 1 (Figure 18-10),
the ECCP1ASE bit will remain set for as long as the
cause of the shutdown continues. When the shutdown
condition clears, the ECCP1ASE bit is cleared. If
P1RSEN = 0 (Figure 18-11), once a shutdown condi-
tion occurs, the ECCP1ASE bit will remain set until it is
cleared by firmware. Once ECCP1ASE is cleared, the
Enhanced PWM will resume at the beginning of the
next PWM period.
Independent of the P1RSEN bit setting, if the
auto-shutdown source is one of the comparators, the
shutdown condition is a level. The ECCP1ASE bit
cannot be cleared as long as the cause of the shutdown
persists.
The Auto-Shutdown mode can be forced by writing a ‘1’
to the ECCP1ASE bit.
18.4.8 START-UP CONSIDERATIONS
When the ECCP1 module is used in the PWM mode,
the application hardware must use the proper external
pull-up and/or pull-down resistors on the PWM output
pins. When the microcontroller is released from Reset,
all of the I/O pins are in the high-impedance state. The
external circuits must keep the power switch devices in
the OFF state until the microcontroller drives the I/O
pins with the proper signal levels, or activates the PWM
output(s).
The CCP1M<1:0> bits (CCP1CON<1:0>) allow the
user to choose whether the PWM output signals are
active-high or active-low for each pair of PWM output
pins (P1A/P1C and P1B/P1D). The PWM output
polarities must be selected before the PWM pins are
configured as outputs. Changing the polarity configura-
tion while the PWM pins are configured as outputs is
not recommended since it may result in damage to the
application circuits.
REGISTER 18-3: ECCPxAS: ENHANCED CCPx AUTO-SHUTDOWN CONTROL REGISTER
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
ECCPxASE ECCPxAS2 ECCPxAS1 ECCPxAS0 PSSxAC1 PSSxAC0 PSSxBD1 PSSxBD0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 ECCPxASE: ECCPx Auto-Shutdown Event Status bit
1 = A shutdown event has occurred; ECCPx outputs are in a shutdown state
0 = ECCPx outputs are operating
bit 6-4 ECCPxAS<2:0>: ECCPx Auto-Shutdown Source Select bits
111 = FLT0 or Comparator 1 or Comparator 2
110 = FLT0 or Comparator 2
101 = FLT0 or Comparator 1
100 = FLT0
011 = Either Comparator 1 or 2
010 = Comparator 2 output
001 = Comparator 1 output
000 = Auto-shutdown is disabled
bit 3-2 PSSxAC<1:0>: Pins A and C Shutdown State Control bits
1x = Pins A and C tri-state
01 = Drive Pins A and C to ‘1’
00 = Drive Pins A and C to ‘0’
bit 1-0 PSSxBD<1:0>: Pins B and D Shutdown State Control bits
(1)
1x = Pins B and D tri-state
01 = Drive Pins B and D to ‘1’
00 = Drive Pins B and D to ‘0’
Note: Writing to the ECCP1ASE bit is disabled
while a shutdown condition is active.