User Manual

CompactRF
TM
Operating Manual: Serial Interface 43
B. Serial Interface
Modem
(DCE)
Signal
Host
Microprocessor
(DTE)
1

DCD
→
IN
2

RX
→
IN
3
←
TX

OUT
4
←
DTR

OUT
5

SG
→
IN
6

DSR
→
IN
7
←
RTS

OUT
8

CTS
→
IN
Arrows denote the direction that
signals are asserted (e.g., DCD
originates at the DCE and tells the
DTE that a carrier is present).
The CompactRF
TM
uses 8 pins on its 36 pin header for asynchronous serial
I/O. The interface conforms to standard RS-232.
The signals in the asynchronous serial interface are described below:
DCD Data Carrier Detect - Output from Module - When asserted (positive
voltage), DCD informs the DTE that a communications link has been
established with another CompactRF
TM
.
RXD Receive Data - Output from Module - Signals transferred from the
CompactRF
TM
are received by the DTE via RX.
TXD Transmit Data - Input to Module - Signals are transmitted from the DTE
via TX to the CompactRF
TM
.
DTR Data Terminal Ready - Input to Module - Asserted by the DTE to inform
the modem that it is alive and ready for communications.
SG Signal Ground - Provides a ground reference for all signals transmitted by
both DTE and DCE.
DSR Data Set Ready - Output from Module - Asserted by the DCE to inform
the DTE that it is alive and ready for communications. DSR is the modem’s
equivalent of the DTR signal.
RTS Request to Send - Input to Module - A “handshaking” signal which is
asserted by the DTE when it is ready. When hardware handshaking is used,
the RTS signal indicates to the DCE that the host can receive data.
CTS Clear to Send - Output from Module - A “handshaking” signal which is
asserted by the DCE when it has enabled communications and transmission
from the DTE can commence. When hardware handshaking is used, the
CTS signal indicates to the host that the DCE can receive data.
Notes: It is typical to refer to RXD and TXD from the perspective of the DTE. This should
be kept in mind when looking at signals relative to the modem (DCE); the modem
transmits data on the RXD line, and receives on TXD.
“DCE” and “modem” are often synonymous since a modem is typically a DCE device.
“DTE” is, in most applications, a device such as a host microprocessor.