M48A-000-DIL RADIOMETRIX, M48A-000-DIL Datasheet - Page 3

• 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

Application Information
What can you do with an M48A ?
The M48A is a 4800 baud radio modem, compatible with narrowband radios.
Just a faster i1200, or a simpler RPM1 ? ....... not quite.
What does an M48A do ?
The interface
RX flow. Goes 'high' when the device has valid data to output
TX flow. High when the transmit buffer is ¾ full, low when empty (“CTS” out)
RX hold. When pulled low, prevents device from outputting data (“RTS” in)
Buffers
Radiometrix Ltd
12. A simple addressing structure is included in the datastream.
13. OSC1, 2 require a 19.6608MHz fundamental mode crystal, a series 100 ohm resistor from OSC2,
14. DFLT0 DFTL1
15. TX_inhibit is only sampled as the transmitter is initialising (and before a carrier is being emitted). It is
16. The –SS (Shrink Small Outline) package has 2 extra pins. See figure 3 in 7 for further details.
In the simplest possible sense, the M48A is just a radio modem baseband device. It provides an
interface between a user's asynchronous (“RS232 type”) serial port and the audio channel of a low
power radio module.
The M48 will transparently handle a half duplex serial stream at 4800 baud, buffering framing and coding
the data into a baseband signal that a narrowband wireless module can handle. At the receive end it
decodes the audio signal back into serial data. The timing requirements of the radio are allowed for with
internal FIFO buffers, while the noisy imperfect radio baseband path is hidden from the user behind S/N
efficient bit coding and data packetisation, with frame synchronisation and a CRC error detection
protocol.
An M48 can be used with just two serial data lines (TXD, RXD). In many applications that is sufficient. If
data is being sent in both directions (half-duplex) however, it is necessary to allow for the turnaround
time (transmit to receive or vice versa) as the M48 cannot handle transmit data input while it is decoding
receive data. (Also, in advanced modes, such as when user interface data rate is higher than 4800 baud
(see later), then transmit data hand-shaking is needed)
In these cases it is useful to have more information as to the status and timings of the link. The M48
provides additional 'handshaking' lines:
As alluded to earlier, data into and out of the M48 is buffered through a pair of small FIFOs. On the
transmit path a 128 byte buffer is used, while on receive a 64 byte buffer is implemented. These buffers
actually occupy the same memory space on-chip, so the part cannot receive and output serial data .
Transmit operations will always over-ride receive. A byte sent to the device will clear the receive buffer,
even if it contains valid data. (An algorithm which reads the 'RX flow' signal can prevent this occurring)
In simple, transparent mode these buffers are invisible to the user.
Units may be programmed onto one of 254 addresses
Address 0 is a broadcast 'all units' address
Address 255 is reserved (Units are supplied set to adr1 = 0, adr2,3,4 and adr_tx =1)
and a pair of 15pF caps : from the crystal pins to 0V
high high : slow timing
low high : tba
high low
high high : tba
These pins have internal pullups. They are only read at power-up, if the unit has not been
programmed. They are also read on execution of a DEFAULT command
ignored during constantly streaming data (ie: once the transmitter has activated)
: tba
(20mS, 50mS, 20mS)
M48A Modem Data Sheet
(“DTR” out)
already
page 3