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DO (Data Out) buffer
When RF data is received, the data enters the DO buffer and is sent out the serial port to a host device. Once the DO
Buffer reaches capacity, any additional incoming RF data is lost. The DO buffer stores at least 2.1 KB.
Two cases in which the DO Buffer may become full and possibly overflow:
1. If the RF data rate is set higher than the interface data rate of the module, the module will receive data from the
transmitting module faster than it can send the data to the host.
2. If the host does not allow the module to transmit data out from the DO buffer because of being held off by
hardware or software flow control.
Hardware Flow Control (RTS). If RTS is enabled for flow control (RT Parameter = 2), data will not be sent out the DO
Buffer as long as RTS (pin 10) is de-asserted.
Software Flow Control (XOFF). XON/XOFF software flow control can be enabled using the FL (Software Flow Control)
Command. This option only works with ASCII data.
Transparent Operation
By default, XTend RF Modules operate in Transparent Mode. The modules act as a serial line replacement - all UART
data received through the DI pin is queued up for RF transmission. When RF data is received, the data is sent out the
DO pin.
When the RO (Packetization Timeout) parameter threshold is satisfied, the module attempts to initialize an RF
transmission. If the module cannot immediately transmit (for instance, if it is already receiving RF data), the serial
data continues to be stored in the DI Buffer. Data is packetized and sent at any RO timeout or when the maximum
packet size is received.
The module operates as described above unless the Command Mode Sequence is detected. The Command Mode
Sequence consists of three copies of the command sequence character [CC parameter] surrounded by the before and
after guard times [BT and AT parameters].
If the DI buffer becomes full, hardware or software flow control must be implemented in order to prevent overflow
(loss of data between the host and module).
API Operation
API (Application Programming Interface) Operation is an alternative to the default Transparent Operation. The API is
frame-based and extends the level to which a host application can interact with the networking capabilities of the
module. When in API mode, all data entering and leaving the RF module is contained in frames that define operations
or events within the module.
Transmit Data Frames (received through the DI (Data In) pin) include:
•
16-bit address
Receive Data Frames (sent out the DO (Data Out) pin) include:
•
Showing a received RF packet (16 bits only)
•
Response to a TX (Transmit) packet
•
Showing events such as hardware reset, watchdog reset, asynchronous events, etc.
The module will send data frames to the application containing status packets; as well as source, RSSI and payload
information from received data packets.
API operation option facilitates many operations such as the examples cited below:
XTend RF Module User Guide
Transparent Operation
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