Nuts & Volts

■ BY PETER BEST
ARM YOURSELF WITH PHILIPS
MICROCONTROLLERS
This time around, the object of our
affection is the Philips LPC2100
family of 32-bit ARM7 microcontrollers.
In this text, we will focus
specifically on building some
LPC2106 and LPC2136 ARM7 hardware
from scratch. Once the hardware
is assembled, I’ll walk you through
some functionality testing and
introduce you to some of the
hardware and software tools you’ll
need to program and debug the ARM7
microcontrollers.
When we’re confident that all of
our ARM7 hardware design work has
been validated, we’ll look at what it
takes to write some code to access
the features of our newly crafted piece
of 32-bit hardware. I’m not going to
assume (that turns you into a donkey)
that you know anything about ARM
microcontrollers. With that, let’s
begin our design process by gaining
an understanding of the basic
ARM architecture as it applies to
the Philips LPC2100 family of ARM
microcontrollers.
THE LPC2106
Although we will be designing
one-half of our ARM7 support hardware
around the LPC2106, we could
also drop the LPC2104 or LPC2105
into a very similar — if not identical
— design. The LPC2104, LPC2105,
and LPC2106 are pin-to-pin compatible
and are all based on the 16/32 bit
86 April 2006
THE
DESIGN
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
ARM7TDMI-S CPU.
If you’re wondering where the
16-bit functionality resides, the
ARM7TDMI-S CPU core can run in
what is termed THUMB mode, which
is a code efficient 16-bit mode of
operation. I’m going to stick with the
32-bit ARM mode in our scratch-built
projects. So, we won’t be employing
THUMB mode in any of our code
designs.
Compared to standard eight-bit
microcontrollers, the LPC2100 ARM7
devices are Flash and SRAM rich. All
of the aforementioned LPC2100
ARM7 variants come out of the box
with 128KB of Flash. The LPC2104
contains 16KB of SRAM and the
LPC2105 houses 32KB of SRAM.
We’re designing with the Big Daddy
of the bunch, as the LPC2106 is
packing 64KB of SRAM on top of the
128KB of Flash.
The large amounts of Flash and
SRAM are complimented by the
ARM7 CPU’s speed. The ARM7TDMI-S
CPU core is supported by a 128-bit
wide memory interface and an accelerator
subsystem that can execute
32-bit instructions at clock speeds up
to 60 MHz. The LPC2100 devices are
based on Reduced Instruction Set
Computer (RISC) operating principles,
which makes the instruction set
and the hardware that processes the
instruction set simple in comparison
to Complex Instruction Set Computer
(CISC) architected microcontrollers.
CYCLE
IN THE PREVIOUS PAIR OF DESIGN CYCLE COLUMNS, we explored the
nuances of the Freescale MC68HC908MR16.This month, we’re going to up the
ante a bit and jump out of the eight-bit microcontroller universe and warp into
the 32-bit microcontroller sector of the microcontroller galaxy.
Most of the time, when it comes down
to efficiency in computing systems,
simpler is better. In the case of the
LPC2104, LPC2105, and LPC2106, the
previous statement holds true.
A cursory look at Figure 1 will tell
you that the LPC2106 achieves its
blazing speed by tying all of the
ARM7 CPU subsystems together with
high speed busses. Standard microcontroller
crystals are used to feed
the input of the LPC2106’s PLL
(Phase Locked Loop), which is used
to multiply the base crystal oscillator
frequency.
In addition to the standard
microcontroller reset, crystal oscillator,
and external oscillator inputs, the
LPC2106 implements an industry
standard JTAG interface, which allows
external applications to access the
LPC2106’s internals via a piece of
integral JTAG hardware. The LPC2106
can be debugged and programmed
using the microcontroller’s JTAG pins.
The LPC2106 can also be programmed
by activating the on-chip
In-System Programming (ISP) and
In-Application Programming (IAP)
boot-loader firmware. The LPC2106
Boot Loader is used in conjunction
with the LPC2106’s ISP subsystem
and UART0 to program the LPC2106.
Programming Flash program
memory locations using IAP is
performed under user program
control. In either mode — ISP or IAP
— the LPC2106 on-chip Boot Loader