Rainbow Electronics DAB-WLS-C21 (BlueTooth) - Manual (Page 17)

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DSH_BTM402_0v9 BISM2 PA Data Sheet.DOC © 2007 EZURiO Ltd 17
9. Application Examples
9.1 RS232 Modem Signals
A serial port has DTR, DSR, RTS, CTS, DCD and RI control lines. RTS and CTS are locally controlled to
prevent local buffer overflow.
The status of DTR, DRS, DCD and RI can be exchanged with the remote peer device. If for example,
the DTR/DSR lines are to be exchanged between the two peers to simulate the performance of a
physical cable, then it is possible to do so. Refer to the description for S Registers 551, 552 and 553
for more details.
Just as a telephony modem has control and status lines, the Module also provides for 6 control and
status lines as per the table below. The direction column is as seen from the module’s viewpoint.
Direction Function
IN or OUT * RI also known as CI (Ring Indicate)
IN or OUT * DCD (Data Carrier Detect)
IN DSR (Data Set ready)
OUT DTR (Data Terminal Ready)
IN CTS (Clear to Send)
OUT RTS (Request to Send)
* configurable with S register 552
The first four lines are under program control. These use four of the GPIO pins and are mapped to
I/O as per the table below. The last two are under control of the UART driver and their functionality is
always enabled.
Direction Connector Pin Label Function
IN/OUT UART_RI Input/Output from module
IN/OUT UART_DCD Input/Output from module
IN UART_DSR Input to Module
IN/OUT GPIO3/UART_DTR General Purpose I/O (or DTR functionality)
IN/OUT GPIO4 General Purpose I/O
IN/OUT GPIO5 General Purpose I/O
IN/OUT GPIO6 General Purpose I/O
IN/OUT GPIO7 General Purpose I/O
IN/OUT GPIO8 General Purpose I/O
IN/OUT GPIO9 General Purpose I/O
Some serial implementations link CTS and RTS to remove the need for handshaking. EZURiO do not
recommend linking CTS and RTS other than for testing and prototyping. If these pins are linked and
the host sends data at the point that the Bluetooth Serial Module deasserts its RTS signal, then there
is a significant risk that internal receive buffers will overflow which could lead to an internal processor
crash. This will lead to a drop in connection and may require a power cycle to reset the module.
EZURiO recommend that the correct CTS/RTS handshaking protocol be adhered to for proper
operation.