Flow Control - HORNER HE800WCM802 Supplement Manual

WCM802/900

Flow Control

Figure 2.3. Internal Data Flow Diagram (The five most commonly‐used pin signals shown.)
DI (Data In) Buffer and Flow Control
When serial data enters the WCM802 / WCM900 Module through the DI Pin, then the data is
stored in the DI Buffer until it can be transmitted.
When the RO parameter threshold is satisfied (refer to Transmit Mode section [p11] and
command descriptions [17] 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. 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 WCM802 / WCM900 OEM RF
Module).
How to eliminate the need for flow control:
1.
2.
Two cases in which the DI Buffer may become full and possibly overflow:
1.
2.
Hardware Flow Control (
default, the module de-asserts (high)
to FT (Flow Control Threshold) and CS (DO2 Configuration) Commands].
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.
Two cases in which the DO Buffer may become full and possibly overflow:
1.
2.
Hardware Flow Control (
not be sent out the DO Buffer as long as
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.
20 JUN 2005
Send messages that are smaller than the DI buffer size. The size of the DI buffer varies
according to the packet size and parity setting used.
Interface at a lower baud rate (BD parameter) than the fixed RF data rate.
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.
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 4) 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.
). When the DI buffer is 17 bytes away from being full; by
to signal to the host device to stop sending data [refer
). If is enabled for flow control (RT Parameter = 2), data will
(pin 5) is de-asserted.
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is re-asserted after