I'd be grateful if anyone can confirm whether, with the CCP module of a
PIC16F818 in "special event trigger" mode, the I/O pin associated with
CCP behaves as a normal digital output controlled by its PORTB bit.

The simulator in MPLAB v7.21 suggests otherwise.  I can demonstrate the
scenario independently of my code by running manual tests on MPSIM using
the SFR window.  When I set TRISB to all zeroes and CCP1CON to any value
from B'00001000' to B'00001111', the PORTB bit associated with the CCP
module (RB2 or RB3 depending on CONFIG word) "sticks" at its previous
value -- any attempts to change it by writing to PORTB have no effect.
When I repeat this test with CCP1CON set to B'00000xxx', all PORTB bits
can be changed freely.

I'd expect the CCP output to override the state of the relevant bit in
the PORTB register in the modes CCP1CON3:CCP1CON0 = 1000, 1001 and 11xx
but *not* in "software interrupt on match" or "special event trigger"
modes (CCP1CON3:CCP1CON0 = 1010 and 1011).  The block diagram of the RB3
pin (Figure 5-11 on page 48 of the PIC16F818 data sheet) backs this up:
in the latter two modes, the value on the PORTB data latch rather than
the CCP output latch should appear on the output pin.

I don't have a device in the PIC16F818 family to hand at the moment, so
I'm unable to establish whether this is a bug in MPSIM or an oddity of
the PIC16F818.  I have previously used "special event trigger" mode in a
PIC16F628 to configure Timer 1 and CCP1 as a 16-bit period counter with
auto-reload whilst also using the RB3/CCP pin as an independent digital
output.  Is there a restriction on this in the PIC16F818 family?

Many thanks in advance for any help.
--
Ian Chapman
Chapmip Technology, UK
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