Circuitry for emulating single chip microcomputer without access to internal buses

摘要

An emulator circuit utilizes an Intel 8031 microprocessor with external address and data buses to emulate an Intel 8051 single chip microcomputer with no external buses by providing external registers into which the contents of the internal 8031 "Port 0" and "Port 2" registers are output and functionally "recreated". The external access (EA) lead is toggled to make the 8031 function as an 8051 during the states in which the 8051 samples its logic levels and destroys port 0 latches if configured as an 8031. Toggling the EA lead to a high level causes outputting the contents of the Port 0 and Port 2 latches to their respective leads. The emulator circuit generates a "Force Ports" pulse that causes the "recreated" port registers or the external circuitry to "force" external logic levels onto the 8031 Port 0 and Port 2 leads. The address latch enable (ALE) signal is delayed until after the Force Ports signal lapses to allow the internal Port 0 logic to generate address outputs on its leads as part of the external address bus.