During psionic combat the creatures involved can engage in no other activity.
The procedure is as follows: Combatants select their defense modes, attack modes, and opponent
(if multiple creatures per side are involved).
This information is recorded, and the defenses and attacks are matrixed to determine results.
Expeditures for defense, attack and combat losses ore noted and token from the appropriate totals of involved creatures.
Psionic combat takes place at a rate of 1 exchange per segment,
10 exchanges per melee round.

If the attention of a creature is distracted by physical attack or spell damage or effect (such as charm hold, etc.)
it cannot engage in attack, although its defenses remain.

Non-psionic creatures can be attacked psionically only by attack mode A, psionic blast.
This attack mode cannot be used by distracted creatures as shown above.
 

Q: During melee, should psionic combat
be resolved before physical attacks, or
during it? If during, how do you tell when
the weapons hit?
A: Psionics are not deadly nor overly
complicated, but the DM must watch melee
a little closer than normal. Characters
can get a maximum of 10 psi attacks
per round, 1 per segment; but "the creatures
involved can engage in no other
activity" (PHB, pg. 116). Interruptions
during psi combat prevent psi attacks,
but defenses are allowed. A demon, for
example, could keep up a psoinic defense
while engaging in hand-to-hand
combat, but could not perform any of its
"At will" spell-like abilities while doing
so; it must drop its psionic defenses to
use its special abilities.
    Weapon speed factors, modified by
the initiative rolls, determine the exact
point in the round at which the attack
occurs, and casting times determine
spell effects in the same way. It is possible
for a creature to psionically attack
and defend at the beginning of a round,
-- with a delay (loss of initiative) equal to
the number of segments spent psionically
attacking.
(Polyhedron #3)

ADQ: If a psionic character does not have 
a defense "up" when psionically 
attacked, how are the results calculated-- 
vs. defenseless psionic, non-psionic, or 
what? 
ADA: The mind of the psionic being 
attacked automatically "puts up" a defense 
-- and the best possible one, at that (DMG 
pg. 79). If the victim possesses no defense 
mode (a rare event, but possible), calculate the 
result as if vs. defenseless psionic. 
(Polyhedron #21)

Q: If a psionic character is surprised by a psionic monster, does
the monster get to attack the character as if the character were
defenseless?

A: No; psionic defenses will go automatically into action once an
attack from another psionic creature gets under way, unless the
character has exhausted all of his defense points.
The "psionic attack on defenseless psionic" table is only used when the target
character or creature has no defense strength left at that time.
(78.16)
 

Q: Shouldn't psionic attacks or defenses put up by experienced
and high-level psionic characters be more effective than those
put up by lower-level characters or creatures?

A: No; just as a sword blow does the same amount of damage
whether the weapon is wielded by a 20th-level Lord or a 1st-level
Veteran (not counting a certain character's bonuses or penalties),
the psionic attacks and defenses of all psionic characters work
the same way and with the same potential power.
(78.16)
 

Q: Can a psionic character cast a spell while employing any sort
of psionic power (attack, defense, or discipline)?

A: A psionic character can maintain a thought shield defense
while fighting, casting a spell, or being involved in some other
strenuous activity. This won't work for any other defense mode
or any attack mode, however; a psionic character cannot mount a
physical attack and a psionic attack at the same time (although
certain monsters, like the intellect devourer, can), and also cannot
employ both a spell and a psionic discipline simultaneously,
since it's impossible to fully concentrate on both activities.
(78.18)

ScottyG wrote:
Gary, it's stated that psionic combat occurs at a rate of one exchange/segment.
Does that include psionic attacks on a non-psionic?
Would a mind flayer get 10 mind blasts in a round against a party?
Scott
 

Howdy!

A mind flayer attacking non-psionic targets is not combat, and as they are not psionically able, there is but one attack in a round, just as with most characters attacking physicaly.

BTW, have I mentioned that I regret ever including psionics in AD&D?

Heh,
Gary