Radiometrix Ltd, SpacePort Modem
page 6
2.3 HOST TO SPACEPORT DATA TRANSFER
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 (10k
Ω).
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 (10k
Ω).
2.6 FORCING SPACE 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 pulled high to force the SPM to shutdown into low
power sleep mode.
HOST DRIVEN WAKE
The WAKE pin may either be driven by the host (recommended) or pulled up to 0V via a suitable
resistor (10k
Ω).