>
> > One of the instructions I remember is CIA for Complement and Increment
> > Accumulator (negate the accumulator).
>

Never a PDP8 user (except to play "Space War") but I liked
TAD =3D
Two's complement add.
A reminder that you were dealing with signed numbers AND that there was NO
subtract.
To subtract you use Harolds CIA and then you TAD

Basic instructions[edit
<http://en.wikipedia.org/w/index.php?title=3DPDP-8&action=3Dedit&section=3D=
8>]000
- AND - AND <http://en.wikipedia.org/wiki/Bitwise_operation> the memory
operand with AC.       001 - TAD - Two's complement
<http://en.wikipedia.org/wiki/Two%27s_complement> ADd
<http://en.wikipedia.org/wiki/Addition> the memory operand to <L,AC> (a *12
bit* signed value (AC) w. carry in L).010 - ISZ - Increment the memory
operand and Skip next instruction if result is Zero.011 - DCA - Deposit AC
into the memory operand and Clear AC.100 - JMS - JuMp to Subroutine
(storing return address <http://en.wikipedia.org/wiki/Return_address> in
first word of subroutine!).101 - JMP - JuMP.110 - IOT - Input/Output
Transfer (see below).111 - OPR - microcoded OPeRations (see below).
Harold's CIA is actually a macro :-)
It's CMA + IAC from the group 1 subset of the OPR instruction above

7200 - CLA - Clear Accumulator7100 - CLL - Clear the L Bit          7040 -
CMA - Ones Complement Accumulator7020 - CML - Complement L Bit         7001
- IAC - Increment <L,AC>7010 - RAR - Rotate <L,AC> Right7004 - RAL - Rotate
<L,AC> Left7012 - RTR - Rotate <L,AC> Right Twice7006 - RTL - Rotate <L,AC>
Left Twice7002 - BSW - Byte Swap 6-bit "bytes" (PDP 8/e and up)


                Russell
--=20
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