M48A-000-DIL RADIOMETRIX, M48A-000-DIL Datasheet - Page 4

• Manufacturer Part Number: M48A-000-DIL
• Description: IC, CONTROLLER, SERIAL MODEM, 20DIP
• Manufacturer: RADIOMETRIX

Specifications of M48A-000-DIL

• Baud Rate: 4800baud
• Supply Voltage Range: 4.5V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: DIP
• No. Of Pins: 20
• Controller Type: MOSFET
• Data Format: Asynchronous

Speed
Crystal frequency
[ slower clock frequencies will also allow operation on lower power supply voltages than the basic +5v
Radio interface
[ Unless otherwise programmed, all units send on address 1 and receive on address 0 (broadcast) and
M48 also has an auxiliary serial output (only) pin, which is used to allow the user to send serial programming
Programming the M48A
In the simplest case an M48 can be used 'as supplied' as a straight forward transparent data link. There are,
however, a number of further options and features which require the user to program parameters into the
device.
Normal transparent data mode is referred to as 'data' mode. To program the device, it is necessary for it to
be in 'setup' mode.
The device is programmed through the RS232 port (without needing extra 'pgm mode' switching pins or
extra hardware). The command set uses simple readable ASCII words, and decimal or hex numbers. All
commands are in upper case.
When in setup mode the usual radio data communication functions are suspended, but limited one-packet-
at-a-time non-transparent operation is possible, via special commands.
The setup mode is activated by means of a 'break / respond' protocol
entering setup
Radiometrix Ltd
normally specified, See Microchip PIC16F648A data sheet for more information ]
address 1 ]
In normal usage the M48 uses a 19.6608MHz crystal for a basic 4800 baud transparent throughput.
However, elementary communication theory tells us that ultimate range and S/N performance
(sensitivity) relates to bandwidth, and hence data rate.
In applications where ultimate range matters more than a fast data path the M48 can be fitted with
slower clock crystals. In these cases the fundamental link data rate is reduced (and other timing
parameters scaled accordingly) but the link range will be increased.
The raison d'être of the M48 device is to insulate the user from the peculiarities and limitations of the
radio module's audio path. While a detailed analysis of the over-the-link signals is not intended, a basic
overview may be useful:
Three signals connect the modem chip to the radio: tones_out, tones_in and n_txe.
All are digital levels (so connection must be made to the digital baseband pins of the radio, not the low
level analogue connections).
At the bit-level the radio link signal generated by the M48 is a proprietary biphase (synchronous)
bitstream with a maximum frequency component of 3.2KHz. There is a pseudo-random data whitening
function applied to the data, but the code still does not have a perfect 50:50 mark space balance, so
should be considered a DC coupled signal. At the receiver end a conventional averaging data extractor
will function but a quasi-dc coupled (peak detecting) type, such as the Radiometrix QR96, will give
optimum performance.
The data stream is further formatted into packets. Each packet contains a framing sequence, address
and status information, a CRC and 1-16 data payload bytes. Transmitter on-time delay is allowed for by
the addition of a preamble sequence, while during continuous data transmission the packets are
transmitted end-to-end.
strings to the associated radio module through the device.
:
user generates a 'break' (long 'space' condition)
M48 sends two characters, an @ and a random printable ASCII character
user sends back the random character
M48 replies with a login message “M48 SETUP” and enters setup mode
19.6608MHz Data rate 4800 baud
9.8304MHz
4.9152MHz
2.4576MHz
Data rate 2400 baud
Data rate 1200 baud
Data rate
600 baud
M48A Modem Data Sheet
Sensitivity +0dB
Sensitivity +3dB
Sensitivity +5dB
Sensitivity +7dB
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