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What’s New – Pep/9 CPU Simulator

Version 9.0beta1

Version 9.0beta1 is the first release of the Pep/9 CPU simulator for use with the fifth edition of Computer Systems. Pep/9 CPU differs from Pep/8 CPU as follows:

  • There is a new status bit called the shadow carry. The shadow carry bit is invisible to the programmer at level ISA3, but is visible at level Mc2. In Pep/8 CPU without the shadow carry, the carry bit must be saved when an internal addition occurs, for example when incrementing the program counter, and restored for implementation of an instruction. In Pep/9 CPU, the shadow carry is used for internal operations, which does not disturb the carry bit. Hence, the carry bit need not be saved and restored.
  • Pep/9 CPU now offers support for two designs — the organization with the original one-byte data bus and the modification with the two-byte data bus. Users can switch between both models in the same application.

Other features of Pep/9 CPU are unchanged. Specifically, users can control the data paths interactively, can write and test microcode programs, and can copy the interactive settings to a line of microcode with the click of a button. The application is a modification of the latest version of the Pep/8 CPU application.

This beta 1 version is feature-incomplete. All the features of the one-byte data bus are available, as they are with the latest version of Pep/8 CPU. Also, the model of the two-byte data bus is complete and functional. Students can write and test microprograms with the two-byte data bus. However, the view is incomplete, so students cannot yet interactively control the data path or see the data flow visually in the data section.