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What’s New – Pep/9 Assembler and Simulator

Version 9.1

Fixed a bug that did not allow user-defined trap instructions in some situations.

Version 9.0

Version 9.0 is the first release of the Pep/9 assembler and simulator, for use with the fifth edition of Computer Systems. Pep/9 differs from Pep/8 as follows:

  • The return statement RET replaces the old statement RETn. Local variables are now explicitly deallocated with the ADDSP instruction.
  • Input/Output is memory-mapped. CHARI and CHARO are no longer in the instruction set. CHARI is replaced by a load byte from the input device address and CHARO is replaced by a store byte to the output device address.
  • Pep/9 has a new compare byte instruction CPBr that sets the status bits without regard to the high-order byte of the register, and a new trap instruction HEXO that outputs a word as four hexadecimal digits.
  • The instruction mnemonics are improved and more consistent with each other. For example, the load word instruction mnemonic is LDWr and the load byte instruction mnemonic is LDBr.

Other features of Pep/9 are unchanged. Specifically, the machine has the same eight addressing modes, the same addressing-aaa fields, the same register-r fields, etc. The application is a modification of the latest version of the Pep/8 application.