Download Full paper

Real-Time Data Acquisition and DSP Systems
Mihai V. MICEA
the DAQ that implements the communication interface is the ICOMM module (see
Figure 2-9).
Data communication between the DAQ and the controlling system (DSP) solves
a two-folded issue: (a) to provide a proper hardware/software infrastructure for data
and command exchange and (b) to provide appropriate mechanisms for fetching the
acquisition results when ready into the DSP.
There is a wide range of standard communication interfaces currently available
for the ICOMM implementation, depending on the DSAPS system architecture and
on the application requirements. Table 2-4 synthesizes the most common types of
communication interface used for data/command exchange in DSAPS.
Table 2-4. Standard communication interfaces for DSAPS
Standard
RS-232
(TIA/EIA232-F)1
Type
Serial data
link
Performance
19,200 bps at 16.5 m
(115,200 bps max.)
RS-422
(TIA/EIA422-B)
Differential
serial data
link
RS-485
(TIA/EIA485-A)
Differential
serial data
link
10 Mbps (max.) at
13.2 m;
100 kbps at 132 m
(max.)
Same as above
USB
Universal
Serial Bus
FireWire
High speed
(IEEE 1394a) serial bus
18
10÷100 kbps (low
speed), 0.5÷10 Mbps
(medium speed),
25÷500 Mbps (high
speed);
5 m max. cable length
between peers
Up to 400 Mbps at
4.5 m cable length
Observations
Single-ended, point-to-point
interface.
Supports simplex, half-duplex
and full-duplex type channels
[33].
Multi-drop (multiple receiver
operation), balanced interface
[33].
Balanced interface, multipoint
operation, operation from a
single +5V supply, up to32
transceiver loads (unit loads)
[33].
Supports up to 127 physical
devices in a hierarchic
configuration.
2 data (differential signals) + 2
power lines.
Robust communication protocol
(CRC, error handling/recovery,
etc.) [34].
Tree-structured multipoint
configuration.
6 signal lines: 1 pair for
peripheral power + 2 pairs for
data transport.
Supports hot-swapping, plugand-play and automatic
configuration.
Three-layered communication
protocol, with isochronous
channels [35, 36].
Digital Signal Acquisition and Processing Systems