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The module UART performs tasks, such as timing and parity checking, that are needed for data communications.
Serial communications depend on the two UARTs to be configured with compatible settings (baud rate, parity, start
bits, stop bits, data bits).
Flow control
Internal Data Flow Diagram (The five most commonly-used pin signals shown)
DI (Data In) buffer and flow control
When serial data enters the module through the DI pin (pin 5), the data is stored in the DI Buffer until it can be
processed.
When the RB and RO parameter thresholds are satisfied, the module attempts to initialize an RF connection. If the
module is already receiving RF data, the serial data is stored in the module's DI Buffer. The DI buffer stores at least 2.1
KB. 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 RF module).
How to eliminate the need for flow control:
1. Send messages that are smaller than the DI buffer size. The size of the DI buffer varies according to the packet size
(PK parameter) and the parity setting (NB parameter) used.
2. Interface at a lower baud rate (BD parameter) than the RF data rate (BR parameter).
Two cases in which the DI Buffer may become full and possibly overflow:
1. If the serial interface data rate is set higher than the RF data rate of the module, the module will receive data from
the host faster than it can transmit the data over-the-air.
2. If the module is receiving a continuous stream of RF data or if the module is monitoring data on a network, any
serial data that arrives on the DI pin (pin 5) is placed in the DI Buffer. The data in the DI buffer will be transmitted
over-the-air when the module no longer detects RF data in the network.
Hardware Flow Control (CTS). When the DI buffer is 17 bytes away from being full; by default, the module de-asserts
CTS (high) to signal to the host device to stop sending data [refer to FT (Flow Control Threshold) and CS (GPO1
Configuration) Commands]. CTS is re-asserted after the DI Buffer has 34 bytes of memory available.
Software Flow Control (XON). XON/XOFF software flow control can be enabled using the FL (Software Flow Control)
Command. This option only works with ASCII data.
XTend RF Module User Guide
Flow control
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