Fast forward through a career of programming that included authoring some books on microcontroller programming (see Resources), starting a small design house (Sc Tec), and finishing a post- graduation program at CEFET-SC (another Brazilian
university located in Florianopolis). This was in 2008, when
I had more contact with programmable logic and VHDL
and my curiosity was peaked. Years later in 2016, I found a
very affordable FPGA (Field-Programmable Gate Array) kit
and decided to give it a chance, and started learning more
about FPGA technology.
What would be better than designing a softcore to
learn more about VHDL (VHSIC hardware description
language), FPGAs, and microprocessor cores themselves?
I ended up choosing a modern Z-80 relative: the Zilog
Z8 Encore! (a.k.a., eZ8; Figure 1b). It’s an eight-bit
microcontroller core with a simple -- yet powerful --
instruction set and a very nice on-chip debugger. With its
lightweight IDE (integrated development environment) and
free ANSI C compiler, it is an excellent project to learn
(and also teach) about embedded systems.
Before diving into the depths of the core operation,
VHDL, and FPGAs, let’s take a glance on the Zilog Z8
Zilog Z8 Encore!
The eZ8 is an eight-bit microcontroller family based on
Zilog’s successful Z8 family and on the great Z-80 heritage.
It features a Harvard CISC machine with up to 4,096 bytes
of RAM (file register and special function registers area), up
to 64 KB of program memory (usually Flash memory), and
up to 64 KB of data memory (RAM). The eZ8 core also
includes a vectored interrupt controller with programmable
priority and an on-chip debugger which communicates
with the host computer using asynchronous serial
communication. These microcontrollers are packed with a
very nice peripheral set, ranging from versatile 16-bit timers
to motor control timers, from multiple UARTs (IrDA ready) FIGURE 1C. FPz8 on an FPGA.
FIGURE 1B. Zilog eZ8.
FIGURE 1A. The Zilog Z-80A (courtesy of Wikimedia Commons).
42 July 2017
My love affair with microcontrollers and
microprocessors began back in 1988 when I was
working toward a technical degree at CEFET-PR
(a four year Brazilian secondary/technical school
and university located in Curitiba). I began by
learning the basics while exploring the classic
Zilog Z-80 (Figure 1a).
By Fabio Pereira