FIRMWARE DESCRIPTION
Data Mode
26
2.10
•
19.01.2007
3.3.4.1 Usage of RS-232 interface
3.3.4.1.1 Connection of the interface
The RS-232 interface is operated in DCE mode and therefore behaves like the RS-232 port
of a modem, i.e. DCDIO and RIIO are outputs of HW 86012/22.
3.3.4.1.2 Interface parameters
The baud rate of the RS-232 interface is selected using the SPBD configuration command.
The actual baud rate can be retrieved with the GPBD command. A list of available baud
rates is shown in response to the IPBD command.
The baud rate setting is a local matter, i.e. the two peers of a connection may use different
baud rates at their ends.
3.3.4.2 Flow
Control
For flow control on the RS-232 interface the HW 86012/22 uses hardware handshake
(RTS/CTS).
The hardware handshake signals are active low (usual polarisation in TTL level RS-232
interfaces).
The following description applies to hardware handshake.
Whenever the host deactivates RTSI (RTSI goes high), the HW 86012/22 will stop output of
data after the current data byte. Due to pipelining it may happen that some additional bytes
are output before the module stops. Data output is resumed as soon as the module senses
an active RTSI again.
Whenever HW 86012/22 deactivates CTSO (CTSO goes high), the host shall stop output of
data. HW 86012/22 tolerates up to 16 bytes being output by the host after deactivation of
CTSO has occurred. The module activates CTSO again as soon as it is ready to accept
more data from the host.
RTS/CTS handshake is used for local flow control between the module and the connected
host and not directly inter-worked through the DECT link.
In case the host is not ready to accept data from the module and has deactivated RTSI, the
module continues to accept data from its peer until its internal data buffers are filled. Then it
will apply DECT flow control which stops data transmission from the peer.
Hardware flow control can be switched by using the command <SPCOM>.
The peer module continues to accept data from its host (the peer host), until its internal data
buffers are filled. Finally the peer module deactivates CTSO. This signals the peer host to
stop data transmission.
When the host gets ready to accept data and has activated RTSI, the internal data buffers of
the modules are emptied before the peer module activates CTSO. This signals the peer host
to resume data transmission.