Ziatech Corporation ZT 8809A, Руководство по эксплуатации

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CPU Description
V20 OVERVIEW
The microprocessor on board the ZT 8809A is an NEC V20, which is
an 8088 compatible microprocessor with a 16-bit internal and 8-bit
external data bus.
The V20 executes all code written for the
8088/8086 family of microprocessors and includes a superset of their
instruction set. Mnemonics and execution times differ from those of
the 8088/8086 family. Overall program execution will be faster in
most cases.
Performance enhancements provided by the V20 are due to such
architectural features as a dual 16-bit internal data bus, high-speed
effective address generation, high-speed multiplication/division algo-
rithms, and additional hidden temporary registers. The more powerful
instruction set of the V20 includes bit processing, packed BCD opera-
tions, move string, stack manipulation, and 8080 emulation mode.
The V20 supports both byte (8-bit) and word (16-bit) data types. Any
16-bit memory data fetch or write cycle is automatically performed as
two 8-bit transfers, where the least significant byte of the word is
stored in the lower address location and the most significant byte in
the next higher address location.
The V20 consists of two main functional blocks: the Bus Control Unit
(BCU) and the Execution Unit (EXU). The EXU is responsible for
the execution of all instructions, for providing data and addresses to
the BCU, and for manipulating the general registers and the flag
register. The EXU is largely isolated from the "outside world."
The BCU is comprised of the segment and communications registers,
the instruction pointer, and the instruction object code queue, as well
as an adder dedicated to the addition of the segment and offset values
for the creation of the 20-bit memory addresses.
The BCU’s
responsibilities include execution of all external bus cycles,
transferring data to and from the EXU on the Arithmetic Logic Unit
(ALU) data bus, and loading or prefetching instructions into the
queue, where they are subsequently fetched by the EXU.
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