The SpacePort Modem (SPM) is a low cost highly integrated OEM bi-directional wireless interface module. The SPM is designed as an OEM product that can be easily incorporated into new and existing designs. The SPM uses addressable data packets with error checking, packet acknowledgements and retransmissions to achieve a reliable invisible wireless data link. Built for ease of use and rapid installation, the serial interface ensures direct connection to microprocessors and microcontrollers while remote configuration enables post installation setup of the modem.

• · Addressable point-to-point.
• · Point-to-Multipoint and broadacast
• · Inverted RS232 interface at TTL level
• · DTE speed 600-115200bps.
• · Air data speed 1200-14400bps.
• . Single 5V or 3.3V supply
• · Flow control - hardware/none.
• · Up to 200m outdoor & 50m indoor range.
• · Built-in command line configuration.
• · Built-in RF link diagnostics.
• · Remote over-air unit configuration.
• · Low operating current. Auto standby mode.
• · Conforms to EN 300 220-3 and EN 301 489-3
• . Dimensions - 23mm X 39mm X 6.5mm

• · PDAs, organisers & laptops
• · Telemetry and telecontrol
• · Handheld / portable terminals
• · EPOS equipment, barcode scanners, belt clip printers, stock control, jo allocation
• · Remote data acquisition system, data loggers
• · Audience response systems
• · In-building environmental monitoring and control systems
• · High-end security and alarm signalling
• · Restaurant ordering systems
• · Fleet management, vehicle data acquisition

INTRODUCTION

The SPM2 is a self-contained radio modem module that requires only a simple antenna, 5V supply and a serial I/O port on a host microcontroller or PC.

The module provides all the RF circuits and processor intensive low level packet formatting and packet recovery functions required to inter-connect any number of microcontrollers in a radio network.

A continuous stream of serial data downloaded by a Host microcontroller into the SPM serial receive buffer is transmitted by the SPM'S transceiver and will "appear" in the serial buffer of the addressed SPM within radio range.

Figure 1: SPM + Host µ-controller
Figure 2: Physical dimensions and pinouts
TECHNICAL SPECIFICATIONS
General
Operating Voltage	5V (standard)
	3.3V (3V version)
Operating Current
Transmitting/Receiving	Average 40mA (Data streaming)
Standby/Power-down	15mA/400mA
Operating Frequency	Single channel 433.92MHz
	To be released on 869.85MHz and 914.50MHz
Operating Temperature	-10 to +55 degrees C
Configuring options	Built-in command line configurator
Interface
Serial Interface	Inverted RS232 at TTL level
Serial Protocol	8 data/1 stop/no parity
Serial Signals	RXD, TXD,CTS, WAKE
Powerdown Control	Via WAKE signal
Serial Handshaking	Selectable as CTS signal or none
DTE Interface Speed	600/1200/2400/4800/9600/14400 19200/38400/57600/115200 bps
Air Interface Speed	1200/2400/14400 bps
Throughput:
Acknowledged	18kbps (max) for standard and 28kbps for fast variant
Un acknowledged	30kbps (max) for standard and 55kbps for fast variant
Receiver
Sensitivity	-95 dBm for 1ppm BER and -90dBm for fast variant
LO leakage (conducted)	-70dBm
Transmitter
Output Power	10mW ERP
2nd harmonics	-46 dB
Approvals	Complies with ETSI EN 300 220-3 (radio), ETSI EN 301 489-3 (EMC)

The SPM is a connection oriented modem module for sending and receiving serial data via an RF communications link.

The SPM handles all necessary protocol related functions of validation and retries to ensure error free and uninterrupted data is sent over the communications link. All data transfers between a pair of SPMS are fully acknowledged, thus preventing the loss of data. Bit coding and checksums are used on the data packets to ensure the validity of the received data at the remote end.

1.1 OPERATING STATES

The SPM has three normal operating states:

· SHUTDOWN
· STANDBY
· CONNECTED

SHUTDOWN
The SHUTDOWN state is entered by asserting the WAKE/DTR input pin. It effectively forces the SPM into a suspended state. No communications can be made with the SPM in this state.

STANDBY
Immediately after power up and during normal operation, the SPM will automatically enter standby mode where it is waiting for a connection request from a remote SPM module.

While in this mode a remote connection request can be received which will place the SPM into a connected state allowing it to then start receiving data from the remote unit. The connected host device can also send data to the SPM via the serial interface which will force the module to send a connection request to the remote SPM module, thus effectively setting up a logical connection between two units and allowing data to be transferred.

CONNECTED
On receipt of a connection request from a remote unit, the SPM immediately enters a connected state. This effectively allows the SPM modems to start sending and receiving data.

In-coming data is sent to the host via the serial port in the same form as it was given to the remote SPM module.

RESET
The Reset signal may either be driven by the host (recommended) or pulled up to Vcc via a suitable resistor (10kW). A reset aborts any transfers in progress and restarts the SPM.

HOST DRIVEN RESET
Minimum low time: 1.0 ms, after reset is released (returned high). The host should allow a delay 1ms after reset for the SPM to initialise itself.

Data is transferred between the SPM and the HOST using an asynchronous serial protocol. The default protocol settings are 8 data bits, no parity and 1 stop bit (8n1). The baud rate setting for the serial interface is user settable from 600bps to 115200bps.

TXD
Data from the connected host is received by the SPM using TXD signal.

CTS
A single handshake line, CTS, controls the flow of data into the SPM. The serial receive buffer of the SPM is 96 bytes deep. The CTS will be asserted by the SPM when the receive buffer hits approximately 66% full. It is advisable to limit the number of characters sent to the SPM after the CTS control line is asserted. This will help to reduce the possibility of lost data due to internal buffer overruns in the SPM. The SPM will clear the CTS when the internal serial receive buffer falls below 33% full.

RXD
Upon the SPM receiving data from a remote unit, the received data is sent to the connected host device using the RXD signal.

2.4 ENTERING SPACEPORT MODEM CONFIGURATOR

Configuring the SPM is accomplished by using a built-in command line configurator. The configurator is entered by asserting the SETUP input of the SPM while resetting the SPM.

SETUP
Holding SETUP low during a reset cycle will force the modem into the configurator. The state of this input is checked while the SPM starts up from either power on or reset.

HOST DRIVEN SETUP
The Setup pin may either be driven by the host (recommended) to enable host controlled configuration of the SPM or pulled up to VCC via a suitable resistor (10kW).

2.5 FORCING DEFAULT SERIAL BAUD RATE

Asserting this pin low forces the SPM to startup with a default baud rate of 9600bps, 8 data, one stop and not parity.

DEFAULT
During a RESET the HOST must hold DEFAULT low to force the SPM serial interface to default to 9600bps. This is ideal if the serial baud rate has been forgotten or incorrectly set.

HOST DRIVEN DEFAULT
The DEFAULT pin may either be driven by the host (recommended) or pulled up to VCC via a suitable resistor (10kW).

2.6 FORCING SPACEPORT MODEM IN TO SLEEP MODE

Asserting the WAKE input high forces the modem into a low power sleep mode. This effectively shuts down the SPM and prevents it from sending or receiving any data. It is a method for conserving power when the modem is not required.

WAKE/DTR
During normal operation WAKE pin can be asserted to force the SPM to shutdown into low power mode.

HOST DRIVEN WAKE
The WAKE pin may either be driven by the host (recommended) or pulled up to OV via a suitable resistor (10kW).

3.1 ENTERING THE CONFIGURATOR

The SPM is configured by entering the built-in software configurator. Current argument can be displayed by entering parameter / command without argument.

Note:
To configure the SPM, the HyperTerminal should be set with the following settings.
Hardware flow control should be disabled. Default baud rate of the SPM is 9600bps. However if the default baud rate of the SPM is changed then the baud rate of the HyperTerminal should be matched or DEFAULT jumper should be connected to force the SPM baud rate to 9600bps.

4. EXTENDED SPACEPORT FEATURES

4.1 THROUGHPUT

The SPM supports two rates, MAX and SLOTS, of over-air throughput. A third rate is also provided which can be used during normal operation, but is specifically supplied for compliance with FCC regulations.

MAX: When set to MAXimum and streaming data at the SPM, the data is sent as quick as possible. For host baud rates of 19200bps and above, data is transmitted continuously with minimal delay between sequential packets. When this occurs, there is effectively no airtime for another pair, operating in close proximity, to transmit without causing collisions. The maximum over-air throughput that can be achieved is 14400bps.

Baud 600,1200,2400,4800,9600,19200,38400,57600,115200
Unit 0 to 15
Site 0 to 7
Shdn on/off
Flow hw/none
Serdly 2 to 255
Retry 1 to 63
Signon on/off

The <PARAMETER> is optional, and if not specified the setting for that command is returned and displayed.

The SPM can be used for point-to-multipoint communications. One module must be considered to be the master, which is used to address up to 15 remote units in any one site.

During normal operation, the base unit can be set to address another unit dynamically by entering the configurator and using the ADDR command to change the unit address. Upon execution of this command, provided the parameters are correct, the configurator is exited immediately. A period ('.') is sent to the connected host device to indicate that the change has been registered and the SPM is now ready for communications to the new unit address.

ADDR is very similar to the Unit command, except that ADDR does not update the stored EEPROM unit value. As the EEPROM has a limited number of write cycles, using ADDR for addressing multiple units in a point to multipoint network is recommended. Also, the ADDR command will exit the configurator immediately, which is requires to resume communications very quickly.

4.4 BROADCAST MULTIDROP

The SPM has a broadcast mutidrop mode which provides a mechanism for building a large networks. This mode of operation is determined by the configuration command keyword ACKMODE being set to OFF.
In broadcast mutidrop mode, the SPM does not implement network layer functionality related to data packet routing, acknowledgement and retries. The connected host device should provide network layer functionality.

The site code and unit address is still used by the radio modem when working in broadcast multidrop mode. For a given multipoint network all radio modems within a group must contain the same site code and unit address.

4.5 RADAR: DIAGNOSTIC TEST

Built into the configurator is a diagnostic test suitable for range testing and link confidence testing. The Radar test effectively sends a small request packet to a remote unit then waits for a reply. The remote unit must not be in the configurator otherwise it will not respond.

Upon receipt of a positive response from the remote unit, a success is recorded before the process is repeated. This test will continue indefinitely until it is ended by a key press.

The SPM's radio decoder module is deliberately non bit error tolerant, i.e. no attempt is made to repair corrupt data bits. All of the redundancy in the code is directed towards error checking. For an FM radio link using short packet lengths, packets are either 100% or so grossly corrupt as to be unrecoverable. By the same reasoning, the Host is not informed or sent corrupt data since corrupt information is of little value. The SPM implements packet acknowledges, timeouts and re-transmission accomplish reliable error handling.