of certain types of events, use of different types of
cards, etc.
In light of all the above the general specifications
of the system developed are the following:
• 32-bit architecture with sufficient memory
for different complex applications and for storing
data.
• Flash memory, RAM and MMC and SD
CARD.
• User interface: keyboard, touch screen
(TFT) and thermal printer.
• Means of payment: readers for magnetic
cards, SAM and contactless cards (MIFARE).
• Communications: RS232, Ethernet, USB-
OTG, RTB Modem and GSM Modem.
• Low consumption, fed by rechargeable
batteries.
• Laptop, implying an integrated architecture
giving a compact and robust footprint, necessary due
to the terminal use conditions.
The main software specifications are an open
operating system with free 32-bit Linux code and the
development of the necessary APIs for controlling
all peripherals and programming particular
applications without needing to have an in-depth
knowledge of the hardware controlled.
The system is used for making money transfers
and as such has to meet the additional security
requisites to suit this circumstance: a) Security, the
terminal cannot be allowed to degrade the security
level of the cards themselves. b) If the terminal is
opened or dismantled, the sensitive information has
to be erased before allowing access. c) Its protection
systems include multiple-tamper-detectors to protect
customers' PINs, magnetic stripe data, application
programme and transaction data.
This paper has been broken down into the
following sections: after this introduction section
two below gives an account of the hardware block
diagram, with a comment on all the modules making
up the design; section 3 deals with the software
architecture; section 4 comments on the results and
winds up the article with the main conclusions.
2 HARDWARE ARCHITECTURE
Figure 1 shows the block diagram of the
implemented hardware system. This block diagram
gives a good idea of the device’s functionality; it
should also be taken into account that the system is
totally reconfigurable at hardware level: for example
the GSM modem could be implemented in a
commercial model instead of the RTB modem,
obviously accompanied by the suitable software.
The system has been designed around a state-of-
the-art microcontroller with a sufficiently wide
range of resources for the design to be optimised.
Freescale’s iMX21 (Freescale Semiconductor, 2004)
microcontroller is the central unit of the POS. This is
a device especially designed for multimedia
applications, with sufficient resources for
implementing the design: ARM9 core, JTAG
connection, timers, equipad, SLCD controller,
SDRAMC, MMC, multimedia accelerator, a
complete memory access interface, bootstrap, etc.
This microprocessor’s wealth of internal resources
has enabled the hardware development of this
system to be greatly simplified.
The following sections comment on the main
characteristics of each one of the blocks of figure 1.
CPU + Memory + Power: power feed control:
As already pointed out, the core of the system is the
IMX21. Its capacities have been optimised in the
interests of achieving the best possible design. This
circuit is fed with 3.2 volts, which is the working
voltage of most of the circuits. The module for the
control of the circuit power-feed is based on C.I.:
TPS 65012.
The system has been equipped with 32 Mb of
FLASH memory and 64 Mb of SDRAM (133 MHz),
sufficient for running the Linux Kernel and
implementing the applications for which the system
has been designed. The FLASH memory is
implemented with the low-consumption integrated
circuit S29GL128M, at 3.0 V
DC
. The SDRAM is
Figure 1: Hardware block diagram.
CPU
RAM
FLASH
MMC
RS232
ETHERNET USB JTAG
MODEM
RTB
/GSM
KEYBOARD
TFT
PRINTER
AUDIO
ISO7811
ISO7816
ISO14443
POWER
CODEC
CPU
RAM
FLASH
MMC
RS232
ETHERNET USB JTAG
MODEM
RTB
/GSM
KEYBOARD
TFT
PRINTER
AUDIO
ISO7811
ISO7816
ISO14443
POWER
CODEC
MULTIFUNCTION SYSTEM BASED ON A STATE-OF-THE-ART MICROCONTROLLER
133