XIB-E【PDF 10/64 页】BOARD INTERFACE ETHERNET

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2.1.2. Flow Control

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DI (Data In) Buffer and Flow Control

When serial data enters the XStream Module through the DI Pin (pin 4), then the data is stored in

the DI Buffer until it can be transmitted.

When the RB and RO parameter thresholds are satisfied (refer to Transmit Mode section [p11]

and command descriptions for more information), the module attempts to initialize an RF

connection. If the module is already receiving RF data, the serial data is stored in the DI Buffer.

The size of the DI Buffer can be determined by issuing the RZ (DI Buffer Size) Command. 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 XStream 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 fixed RF data rate.

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 monitoring data on a network,

any serial data that arrives on the DI pin 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 (

). When the DI buffer is 17 bytes away from being full; by default,

the module de-asserts (high)

to signal to the host device to stop sending data [refer to FT

(Flow Control Threshold) and CS (DO2 Configuration) Commands].

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.

DO (Data Out) Buffer and Flow Control

When RF data is received, the data enters the DO buffer and is then sent out the serial port to a

host device. Once the DO Buffer reaches capacity, any additional incoming RF data is lost. The

size of the DO Buffer can be determined by issuing the RZ (DI Buffer Size) Command, then

multiplying the result by 1.5.

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 (

). If

is enabled for flow control (RT Parameter = 2), data will not

be sent out the DO Buffer as long as

(pin 5) 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.

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