File: CHESS.TX of Disk: Disks/PDP8-Net/diag-games-kermit
(Source file text)
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A SET OF INSTRUCTIONS
FOR PLAYING CHESS (CHECKMO-II) WITH THE PDP-8 COMPUTER
CHEKMO-II Chess Program for the PDP-8 PAGE 1
ABSTRACT
--------
CHEKMO-II is a chess playing program which will run on
any PDP-8 family computer. The program will play either
the white pieces or the black pieces, and will play and
accept all classes of legal moves, including, castling both
short and long, en passant pawn captures, and pawn
promoting moves to any legal promotion piece. The program
prints out its moves in Algebraic Notation, and accepts
moves using Algebraic Notation.
Included in the command structure of the program are
commands which allow you to input board positions using
Forsyth Notation, and get a printout of the board at your
terminal.
EQUIPMENT
---------
CHEKMO-II will run on any PDP-8 family computer with a
minimum of 4k of memory, and an ASR33 Teletype(1) or
equivelent terminal.
EXECUTION TIME
--------------
The time that CHEKMO-II takes to calculate its moves, is
highly dependent upon the position of the pieces. It is
generaly within the range of 20 seconds, to 2 minutes per
move. In "blitz mode" (see the "BM" command), CHEKMO-II
makes its moves much more quickly, but at the cost of
reduced playing strength.
Note: All times quoted are assuming that CHEKMO-II is being
run on a stand alone PDP-8/E(1.2 us Cycle time).
LOADING AND STARTING CHEKMO-II
-------------------------------
The CHEKMO-II binary tape is a standard binary tape and
can be loaded using the BIN Loader program(DEC-08-LBAA-PM),
or the OS8 "ABSLDR" program. The starting address for
CHEKMO-II is 0200. At any time, CHEKMO-II can be halted
and restarted at location 0200.
-- -- -- -- --
(1) Teletype is a registered trademark of the Teletype
Corporation.
CHEKMO-II Chess Program for the PDP-8 PAGE 2
ON LINE OPERATION
-----------------
Before continuing be advised that all lines of input to
CHEKMO-II must be terminated with a carriage return.
Typing a CTRL/U character echos "^U" and erases anything
typed so far on a line. Typing a RUBOUT character deletes
the last character typed and prints a "\" character to
indicate the deletion. CHEKMO-II has an input buffer with
room for 24 characters. If more than 24 characters are
typed on a line(not counting rubouts and the "rubbed out"
characters), a "^U" is printed and the entire line is
deleted.
When CHEKMO-II is started at location 0200 it will
print...
CHEKMO-II
to identify itself and setup the pieces on its internal
board to thier original squares. Then it will ask...
W. YOUR MOVE?
The "W. " at the begining of the line is to indicate
that it is whites move. The "YOUR MOVE?" indicates that
CHEKMO-II is waiting for you to input a move for white,
using modified algebraic notation (Described on Pg 6). If
the move that you type in is illegal or impossible
CHEKMO-II responds with...
?
W. YOUR MOVE?
Asking again for you to type in a legal move. If a legal
move is typed, CHEKMO-II will make the move on its internal
board, then ask...
B. YOUR MOVE ?
CHEKMO-II is now waiting for you to type in a move for
black(note the "B. "). As before, typing in an impossible
move causes CHEKMO-II to...
?
B. YOUR MOVE ?
Ask again for a legal move. A legal move causes
CHEKMO-II to make that move on its internal board, then ask
for a move for white. Play continues in this manner until
a move is made that checkmates or stalemates. At that time
CHEKMO-II will print...
CHECKMATE
CHEKMO-II Chess Program for the PDP-8 PAGE 3
Or
STALEMATE
In either case the final position is then printed
-- ** -- BK -- ** -- **
** -- ** WQ ** -- ** --
-- ** -- ** WK ** -- **
** -- ** -- ** -- ** --
-- ** -- ** -- ** -- **
** -- ** -- ** -- ** --
-- ** -- ** -- ** -- **
** -- ** -- ** -- ** --
CHEKMO-II now restarts itsef at location 0200, and is
ready to play another game.
CHEKMO-II Chess Program for the PDP-8 PAGE 4
SPECIAL COMMANDS
----------------
At any time when CHEKMO-II is waiting for you to type in a
move, you may instead type in one of the 10 special
commands currently implimented. Each special command
consists of 2 characters and is described below.
PW -- CHEKMO-II is instructed to play the white pieces.
Whenever it is whites turn to move CHEKMO-II will
printout and make a move for white instead of
asking "YOUR MOVE ?".
PB -- Same as "PW" except that CHEKMO-II makes a move
for the black pieces every time it is blacks turn
to move.
PN -- CHEKMO-II plays niether white nor black. This
cancels previous "PW" and "PB" commands
BD -- CHEKMO-II will print out the current board
position
MV -- Causes CHEKMO-II to printout and make the next
move for the side whose turn it is
SK -- Skip the move that CHEKMO-II is asking for, and
make it the other sides move.
Note: According to the laws of chess, "The 2
players must alternate in making 1 move at a
time". The SK command is included because it can
somtimes be fun to use in "non serious" games.
RE -- Stands for "Reset" (or "Resign"). It resets
CHEKMO-II's internal board to the initial starting
position, and begins a new game.
BM -- Puts CHEKMO-II into "Blitz mode". In Blitz mode,
CHEKMO-II does not think very deeply about its
moves, but instead, makes them in 3 seconds each
on the average.
TM -- Resets CHEKMO-II to its regular "thoughtful" mode
of play.
IP -- Instructs CHEKMO-II to accept the input of a
position using Forsyth notation(Described on Pg 7)
CHEKMO-II prints a ">" to indicate that it is
ready for you to enter a line. If you violate the
rules of Forsyth notation, an error message is
printed, and CHEKMO-II waits for you to enter the
error line again. If you enter in a good line,
CHEKMO-II prints a ">" and waits for the next
line. When all 8 ranks are entered successfully,
CHEKMO-II Chess Program for the PDP-8 PAGE 5
the board position just inputed gets printed out.
Possible error messages and thier causes are
discribed below.
Message Cause
1? More than 8 squares specified
2? Less than 8 squares specified
3? Piece color not "W" or "B"
4? Unknown piece letter
CHEKMO-II Chess Program for the PDP-8 PAGE 6
ALGEBRAIC NOTATION
------------------
Algebraic notation is the system recommended by the
International Chess Federation(F.I.D.E.), for the recording
of chess moves. Since in regular Algebraic notation, both
upper and lower case letters are used, and since most
teleprinters output only upper case leters, CHEKMO-II uses
a modified form of algebraic notation to accept moves, and
to print out its own moves. This modified Algebraic
notation is described here.
The ranks(horizontal rows of squares) are numbered from 1
to 8 starting from whites side of the board. The
files(vertical rows of squares) are numbered from A to H
starting at the left(blacks right) hand side of the board.
The intersection of the file letter and rank number gives
each square a unique name. For example, In the initial
position, whites king occupies square E1, blacks king
occupies square E8, and the pawn in front of blacks queen
occupies square D7. Whites knight on square B1 and can
move to squares A3 and C3.
A8 B8 C8 D8 E8 F8 G8 H8 BR BN BB BQ BK BB BN BR
A7 B7 C7 D7 E7 F7 G7 H7 BP BP BP BP BP BP BP BP
A6 B6 C6 D6 E6 F6 G6 H6 -- ** -- ** -- ** -- **
A5 B5 C5 D5 E5 F5 G5 H5 ** -- ** -- ** -- ** --
A4 B4 C4 D4 E4 F4 G4 H4 -- ** -- ** -- ** -- **
A3 B3 C3 D3 E3 F3 G3 H3 ** -- ** -- ** -- ** --
A2 B2 C2 D2 E2 F2 G2 H2 WP WP WP WP WP WP WP WP
A1 B1 C1 D1 E1 F1 G1 H1 WR WN WB WQ WK WB WN WR
A move is specified by the square number of the piece
that is moving, an optional "-" or ":", and the square
number that the piece is moving to. If the move gives
check, an optional "+" character after the move is used to
signify that. Using this notation, the 2 possible moves
for whites knight on square B1 would be, B1-C3 and B1-A3.
The symbol "O-O" is used to specify king side castling, and
the symbol "O-O-O" is used to specify queens side castling.
Pawn promotion moves are printed out in the same manner as
any other pawn move, except that they are followed by a "="
and the initial of the piece the pawn is promoting to. For
example, on an empty board, a pawn on A7 would have 4
posible moves,
A7-A8=N A7-A8=B A7-A8=R A7-A8=Q
On input, If no equal sign and initial are specified, the
promotion is assumed to be to a queen.
CHEKMO-II Chess Program for the PDP-8 PAGE 7
FORSYTH NOTATION
----------------
Forsyth notation is a shorthand method of recording or
describing chess positions. Since regular Forsyth notation
uses both lower and upper case letters, and most telletypes
have only upper case letters, CHEKMO-II uses a modified
form of Forsyth notation, a description of which follows.
Using Forsyth notation the board position is described
rank by rank, starting with rank 8. Each rank is described
from left to right in the following manner. If a square is
occupied, the initial for the pieces color(W or B),
followed by the initial for the piece (R,B,K,Q,P or N), are
used to describe that square. Empty squares are indicated
by a number from 1 to 8, equal to the number of empty
squares adjacent to one another. Every square on a rank
must be accounted for in this manner, and thus each rank
must total 8 pieces and/or empty squares.
Here is a position accompanied by its representation in
Forsyth notation...
BR BN BB ** BK ** BN BR BRBNBB1BK1BNBR
BP BP BP -- ** BP BP BP BPBPBP2BPBPBP
-- ** -- ** -- ** -- ** 8
** -- BB -- WP -- ** -- 2BB1WP3
-- ** -- ** -- ** -- BQ 7BQ
** -- WN WP ** -- BN -- 2WNWP2BN1
WP WP WP ** -- ** -- WP WPWPWP4WP
WR -- WB WQ WK WB WN WR WR1WBWQWKWBWNWR
CHEKMO-II Chess Program for the PDP-8 PAGE 8
ERROR HALTS
-----------
There are 2 legitimate error halts possible with
CHEKMO-II
Address Explanation
5004 An unexplaned interrupt has occured. To recover,
press the CLEAR and CONTinue keys(START on a
non-PDP-8/E). If the error persists, try to find
its cause and eliminate it. A likley cause is a
DF32 Disk unit select switch set to the OFF
position.
1761 The position has gotten too complex and
CHEKMO-II's push down list has overflowed. You
Win!!. Just before halting, CHEKMO-II will
printout...
I RESIGN
This error can probably only occur if one or both
sides has queened several pawns. Restart at
location 0200 to start a new game.
Halting at any other address is extremly unlikley, and is
caused either by a hardware failure, or an as yet unknown
program bug.
KNOWN BUGS
----------
There are no known "bugs" in CHEKMO-II Rev#63.
KNOWN DEFICIENCIES
------------------
CHEKMO-II does not recognize the value of passed pawns
until they reach the 6th or 7th rank.
CHEKMO-II has been programed to use the same strategy
throughout the game. This strategy has been optimized for
good play in the Middle-game, and Opening. As a result
CHEKMO-II plays poor moves in some Endgame positions.
If either the white side or the black side becomes
signifigantly more powerfull than the other(about 4 queens)
CHEKMO-II may play some strange, but legal moves. This is
caused by overflow in an internal evaluator routine.