XLR PRO operational design
XLR PRO Radio Frequency (RF) Modem User Guide
23
Upon starting or restarting the XLR PRO, either a TCP or a UDP listener is set up depending on the
IP
parameter. If UDP
data is received or if a TCP connection gets established before the XLR PRO attempts to send data, then the
DX
and
DY
parameters are unused. In this case, the XLR PRO takes the role of a TCP or UDP server. But if the XLR PRO has data to
send before an IP host sends data to the XLR PRO, then
DX
and
DY
determine the destination of that data until the TCP
connection times out or until IP socket mode is restarted, whichever comes first.
Serial communications
Whether the XLR PRO is configured for USB, RS-232, RS-485/422, or IP socket mode, the XLR PRO handles the traffic as
serial data. The XLR PRO handles all serial traffic the same regardless of which interface is being used.
XLR PRO serial buffers
•
Serial receive buffer
When serial data enters the XLR PRO, the data is stored in the serial receive buffer until it can be processed. Under
certain conditions, the XLR PRO may not be able to process data in the serial receive buffer immediately. If large
amounts of serial data are sent to the XLR PRO such that the serial receive buffer would overflow, then new data is
discarded. If using RS-232, this can be avoided by using hardware flow control. Software flow control can be used
regardless of which serial interface is used.
•
Serial transmit buffer
When serial RF data is received, the data is moved into the serial transmit buffer and sent out of the active serial
interface of the XLR PRO. If the serial transmit buffer becomes full and system buffers are also full, then the entire
RF data packet is dropped. Whenever data is received faster than it can be processed and transmitted out the
serial port, there is a potential of dropping data.
XLR PRO serial interface protocols
The XLR PRO supports both transparent and Application Programming Interface (API) serial interfaces.
Transparent operation
When operating in transparent mode, the XLR PRO acts as a serial line replacement. All serial data received through
the serial interface is queued up for RF transmission. When RF data is received, the data is sent out through the active
serial interface. The XLR PRO configuration parameters are configured using the AT command mode interface.
Data is buffered in the serial receive buffer until one of the following causes the data to be packetized and
transmitted:
•
No serial characters are received for the amount of time determined by the
RO
(Packetization Timeout) parameter.
If
RO
= 0, no packetization occurs and characters will be transmitted immediately.
•
The Command Mode Sequence (GT + CC + GT) is received. Any character buffered in the serial receive buffer before
the sequence is transmitted.
•
The maximum number of characters that will fit in an RF packet is received. See the NP parameter.
API operation
API operation is an alternative to transparent operation. The frame-based API extends the level to which a host
application can interact with the networking capabilities of the XLR PRO. When in API mode, all data entering and
leaving the module is contained in frames that define operations or events within the XLR PRO.
Transmit data frames (received through the serial port) include:
•
RF Transmit data frame
•
Command Frame (equivalent to AT commands)