HP 64782, User Manual, Page: 501 / 554

Concepts of the EMSIM and EMRAM
The 6833x processors provide an array of on-chip peripherals which are
configured and used via memory mapped registers. These registers directly
control many aspects of the external operation of the processor. The most
notable of these on-chip peripherals is the SIM (System Integration Module).
For example, address bits A19 through A23 can be configured as either
address bits, chip select control signals, or discrete output port signals.
Selection of these alternative uses drastically changes the external behavior
of the processor. Internal to the processor, the full 24-bit address and bus
control signals are always maintained. What is seen external to the processor
is determined by the current contents of the SIM register set.
Most of the 6833x processors also have internal, on-board, static RAM which
can be configured to be addressable anywhere within the address range. The
processor RAM register set is used to enable this on-board RAM and to define
where it is currently positioned in the 24-bit address space.
The emulator needs access to the full 24-bit address, function codes, and
other control signals for proper operation of the emulation bus analyzer and
the emulation memory system. To provide this access when these signals are
not available external to the processor, an external bus decoder is designed
into the emulator; it recreates these signals.
The following is a view of the emulator implementation:
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