SYBSC IT SEM IV EMBEDDED SYSTEMS UNIT II Processor Family

Get to Know the
Processor
 If you'll be doing any assembly language
programming, you will need to
familiarize yourself with the processor's
architecture and basic instruction
set.
 Everything you need to know about the
processor can be found in the
databooks (Manuals).

Processors in General
 Many of the most common processors are
members of families of related devices
 The most obvious example is Intel's 80x86
family, which spans from the original 8086 to the
Pentium II-and beyond.
 In fact, the 80x86 family has been so successful
that it has spawned an entire industry of
imitators.
 The term processor refers to any of three types
of devices known as
 microprocessors,
 microcontrollers, and
 digital signal processors

Intel's 80188EB Processor
 The processor on the Arcom board is an Intel 80188EB-a
microcontroller version of the 80186.
 In addition to the CPU, the 80188EB contains an interrupt control
unit, two programmable I/O ports, three timer/counters, two serial
ports, a DRAM controller, and a chip-select unit.
 These extra hardware devices are located within the same chip and
are referred to as on-chip peripherals.
 The CPU is able to communicate with and control the on-chip
peripherals directly, via internal buses.
 Although the on-chip peripherals are distinct hardware devices, they
act like little extensions of the 80186 CPU.
 The software can control them by reading and writing a 256-byte block
of registers known as the peripheral control block (PCB).
 The control and status registers for each of the on-chip peripherals are
located at fixed offsets from the PCB base address.
 The exact offset of each register can be found in a table in the
80188EB Microprocessor User's Manual.

Intel's 80188EB Processor:
Databook
 Other things you'll want to learn about the
processor from its databook are:
 Where should the interrupt vector table be located?
Does it have to be located at a specific address in
memory? If not, how does the processor know where to
find it?
 What is the format of the interrupt vector table? Is it
just a table of pointers to ISR functions?
 Are there any special interrupts, sometimes called traps,
that are generated within the processor itself? Must an ISR
be written to handle each of these?
 How are interrupts enabled and disabled (globally and
individually)?
 How are interrupts acknowledged or cleared?

Initialize the Hardware
 The final step in getting to know your new hardware
is to write some initialization software
 During hardware initialization it will be impossible to
avoid using assembly language.
 All processor-based boards require some amount of
software testing to confirm the correctness of the
hardware design and the proper functioning of the
various peripherals.
 The hardware initialization should be executed
before the startup code
 The code described there assumes that the
hardware has already been initialized and concerns
itself only with creating a proper runtime
environment for high-level language programs

Initialize the Hardware: STEP
1
 The first stage of the initialization process is the reset code.
 This is a small piece of assembly (usually only two or three instructions) that the
processor executes immediately after it is powered on or
reset.
 The sole purpose of this code is to transfer control to the hardware
initialization routine. The first instruction of the reset code must be placed at a
specific location in memory, usually called the reset address, that is specified in
the processor databook.
 The reset address for the 80188EB is FFFF0h.
The hardware and software
initialization process

2
 Most of the actual hardware initialization takes place in the second
stage.
 At this point, we need to inform the processor about its
environment.
 This is also a good place to initialize the interrupt controller and
other critical peripherals.
 Less critical hardware devices can be initialized when the associated
device driver is started, usually from within main.
 Processor’s internal chip-select unit (registers) are responsible
for setting up the memory and I/O maps and are part of the
processor‘s internal chip-select unit.
 By programming the chip-select registers, you are essentially waking
up each of the memory and I/O devices that are connected to the
processor
 Each chip-select register is associated with a single "chip enable"
wire that runs from the processor to some other chip.
 The association between particular chip-selects and hardware
devices must be established by the hardware designer.

3
 The third initialization stage contains the
startup code
 Its job is to the prepare the way for code
written in a high-level language.
 Of importance here is only that the
startup code calls main.
 From that point forward, all of your other
software can be written in C or C++.

SYBSC IT SEM IV EMBEDDED SYSTEMS UNIT II Processor Family

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SYBSC IT SEM IV EMBEDDED SYSTEMS UNIT II Processor Family