Specifications

Introduction
FUNCTIONAL BLOCKS
Figure 1-1 illustrates the ZT 8809A’s functional blocks. A brief
description of each block follows.
V20 (uPD70108) Pr
ocessor
The NEC V20 is an 8088-compatible microprocessor with a 16-bit
internal data bus and an 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. Performance enhancements
are provided by way of such architectural features as a dual 16-bit
internal data bus, high-speed effective address generation, and
additional hidden temporary registers. The added instructions include
shift and rotate by immediate value, move string, stack manipulations,
and 8080 emulation mode. The 8080 emulation mode enables existing
8-bit 8080 software to run on new 16-bit hardware with few or no
software modifications.
Memory and I/O Addr
essing
The ZT 8809A comes populated with one 32 Kbyte static RAM and
four 32-pin JEDEC compatible byte-wide sockets. Two of the sockets
accept 16K through 256 Kbyte EPROMs; the other two accept 32K
through 512 Kbyte RAMs. One of the EPROM sockets can also be
configured to accept a 32K or 128 Kbyte RAM.
The full 20-bit address is used for both on-board and off-board
memory accesses, giving the system 1 Mbyte of direct address space.
I/O accesses are accomplished with a 16-bit address, providing
64 Kbytes of I/O space for 16-bit I/O boards or 256 bytes for 8-bit
boards.
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