XTIB-R Digi International/Maxstream, XTIB-R Datasheet - Page 10

• Manufacturer Part Number: XTIB-R
• Description: BOARD INTERFACE 1W RS232/485
• Manufacturer: Digi International/Maxstream

Specifications of XTIB-R

• Accessory Type: Interface Board
• For Use With/related Products: XTend Radios
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: Q2172356

9XTend™ OEM RF Module ‐ Product Manual v2.x4x [2007.01.04]
2.1.2. Flow Control
DI (Data In) Buffer and Flow Control
DO (Data Out) Buffer
Figure 2‐03. Internal Data Flow Diagram (The five most commonly‐used pin signals shown)
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 (refer to ‘Transmit Mode’ section 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 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:
Two cases in which the DI Buffer may become full and possibly overflow:
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.
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:
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.
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© 2007 MaxStream, Inc.
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.
Interface at a lower baud rate (BD parameter) than the RF data rate (BR parameter).
If the serial interface data rate is set higher than the RF data rate of the module, the mod-
ule will receive data from the host faster than it can transmit the data over-the-air.
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.
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.
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.
Chapter 2 ‐ RF Module Operation
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