Specifications

7.2. DESIGN OPTIONS
Low power Communication should consume as little energy as possible to
conserve battery lif e in backup conditions.
Flexible It should be possible to add additional peripherals to the logger
without requiring any hardware or software modifications.
Simple protocol A simple protocol will ensure that it will be convenient to
add additional peripherals. This will also aid debugging and ultimately
make the system more reliable.
Reliable Data transfer should not corrupt the transported data.
Duplex communication The Logger should be able to send and receive
data over the link to send commands to- and receive data from attached
peripherals.
Communication range It is presumed that any additional peripherals will
be located either within the same enclosure, or in close proximity to the
logger module. Thus, communication range is not a significant factor.
Communication speed The bus spee d is not a significant factor as very
low volumes of data are e xpe cted to be exchanged.
The simplest solution for this type of system is thus a bus type interconnect
as it allows additional modules to be added easily. The following systems were
considered:
• Custom design, possibly based around a modified RS232 system.
• RS485
• CAN bus
• SPI bus
• I
2
C (or I2C or IIC) bus
When considering a custom bus design, it is important to consider the
ease of future expansion. Such a bus would make it more difficult for future
designers to extend the system by adding additional peripherals as no official
66