User's Manual

Company Confidential 60 Raveon Technologies Corp.
8. Appendix A. Serial Port Hardware
8.1. Serial Port Data and Handshaking Signals
In computer terminology, the RF modem is considered a “Data Communications
Equipment” device, or DCE. The user’s hardware that the modem is connected
to is considered “Data Terminal Equipment”, or DTE.
Following is a description of how data and control is communicated over the
various serial port signals between the modem (DCE) and another device (DTE)
that the modem’s I/O port is connected to.
TxD (INPUT)
This line is used to transmit data from the DTE to the DCE. It is maintained at a
logical 1 state when nothing is transmitted. If Hardware Flow Control is enabled
in the modem, the terminal will start to transmit data to the modem when a logical
1 is present on all of the following lines:
• Clear To Send (output from modem)
• Request to Send (output from the DTE)
RxD (OUTPUT)
This circuit is used to receive data from the DCE to the DTE. The modem will
start to transmit data to the DTE when a logical 1 is present on all of the following
lines:
• Data Terminal Ready (reply that it is OK to send)
• Data Set Ready (asserted by the modem)
RTS
On this line, the DTE will send a signal when it wants to receive data from the M7
modem. The M7 modem will not output data unless this pin is low, or “Flow
Control” has been disabled in the modem set-up. When a DTE (such as a PC or
microcontroller) wants to stop the flow into it, it negates RTS. Negated "Request
To Send" (digital 1) means "request NOT to send to me" (stop sending). When
the DTE is ready for more bytes it asserts RTS (digital 0) and the flow of bytes to
it resumes. DCE equipment works the same way but sends the stop signal out
the CTS pin. Thus it's RTS/CTS flow control using 2 lines. The user may turn
this feature off or on, using the ATCH command. The default is OFF. To turn it
on, issue an ATCH 1 command.
CTS
This signal is an output from the M7, and it indicates the M7’s ability to send
more data. If the user tries to send more data into the M7 than the M7 can
transmit over the air, it will negate the signal on this pin. The CTS may be
asserted when the serial-port data rate is greater to or equal to the over-the-air