Technical Manual
Table Of Contents
- 1. Introduction
- 2. Hardware
- 3. The A431 Radio Module
- 3.1. About the A431 Radio Module
- 3.2. Functional description
- 3.3. Manufacturing Issues
- 3.3.1. Marking and labeling issues
- 3.3.2. Alignment Range and Switching Range
- 3.3.3. Tuning Procedure
- 3.3.4. Setting Up the Default Parameters
- 3.3.5. Definitions
- 3.3.6. Test Equipment Settings
- 3.3.7. Trimming Elements
- 3.3.8. Adjusting the Receiver Front End
- 3.3.9. Adjusting the VCOs
- 3.3.10. Adjusting the Crystal Reference
- 3.3.11. Checking the Receiver Parameters
- 3.3.12. Checking the Transmitter Parameters
- 3.3.13. Data Transfer Check
- 3.4. PCB Parts Placement
- 3.6. Frequency Reference Specifications
- 3.7. A431 Module’s Photographs
- 4. Software
57
Modulation Technique Used
ware, and takes at most 6 additional milliseconds. If no valid tone is detected, the
unit goes back to sleep, otherwise it tries to decode the frame.
Based on the destination ID, the frame will be identified. If it is not for that particular
unit (own ID), then the microcontroller will cease decoding it and will go immediately
to sleep. The destination ID is positioned very early in the frame header (see also
“Generic Format of a Radio Frame” on page 57).
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
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:
00
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