59
Modulation Technique Used (low speed modem)
to sleep. The destination ID is positioned very early in the frame header (see also
“Generic Format of a Radio Frame” on page 59).
From the above it becomes clear that in order to initiate a communication, a re-
quester must send first a header which is at least 0.5 seconds long: these are called
long header frames
. Of course, after the communication is established the headers
are short, of only 16 bytes (i.e. 8 msec. – called
short header frames
). If a timeout
occurs, the system will restart by sending long header frames.
4.4.2.
Modulation Technique Used (low speed modem)
The communication via radio is made by using a special MSK (Minimum Shift Keying)
scheme; both the encoding and the decoding of the MSK frames is made in soft-
ware—there is virtually no hardware modem. A
zero
bit is transmitted as a sequence
of 250 µs one level followed by a 250 µs zero level, while a
one
bit is transmitted as
a 500 µs one level followed by a 500 µs zero level. A complete sequence of one and
zero level forms a
bit cell
.
This modulation scheme is self-clocked. The transmission speed is content-depen-
dent, varying from 1 kbps (when sending only ones) to 2 kbps (when sending only
zeros). On the average, an 1500 bps transmission speed is reached.
The data interchange between stations is made by means of
frames
. The frames
have a header, a 16 bit-sync character, a data block, and a 16-bit CRC number. The
bytes forming the frame are send synchronously, with no start and/or stop bits. The
data block is assembled after the sync character was detected. The LSB of a byte is
sent first and the MSB is sent last.
4.4.3.
Generic Format of a Radio Frame
The standard frame format used by the A730 family is as follows:
• The frame starts with a header of zeros and there are two header types: long
and short. The long headers are used to wake up a remote station and must
be 140 bytes long, while the short headers are only 16 bytes long.
0
0
0
1
1
1
00
00
.......
00
0xAA DST-H
DST-L SRC-H SRC-L
DLEN
.......
DATA1 DATA2
DATAn CRC-H CRC-L
Data Frame
Summary of Contents for A440
Page 6: ...6 ...
Page 8: ...8 Introduction This manual is intended for the radio approval authorities and laboratories ...
Page 15: ...22 Hardware Figure 7 A440 Back view ...
Page 16: ...23 A440MB Figure 8 A440 Top view Figure 9 A440 Bottom view ...
Page 17: ...24 Hardware Figure 10 A440 Left and Right views ...
Page 18: ...25 A440MB Figure 11 A440 Case opened Figure 12 A440 Motherboard top view ...
Page 19: ...26 Hardware Figure 13 A440 Motherboard bottom view ...
Page 31: ...45 Data Transfer Check 3 6 Frequency Reference Specifications ...
Page 33: ...47 Data Transfer Check Figure 23 A431 Module Bottom view ...
Page 34: ...48 The A431 Radio Module ...
