User Manual

MHX-2400 Operating Manual: Appendix B Serial Interface 29
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 MHX-2400 module uses 8 pins on the header connector for
asynchronous serial I/O. The interface conforms to standard RS-232 signals
without level shifting, so direct connection to a host microprocessor is
possible.
The signals in the asynchronous serial interface are described below:
DCD Data Carrier Detect - Output from Modem - When asserted (TTL low),
DCD informs the DTE that a communications link has been established with
another MHX-2400.
RX Receive Data - Output from Modem - Signals transferred from the MHX-
2400 are received by the DTE via RX.
TX Transmit Data - Input to Modem - Signals are transmitted from the DTE via
TX to the MHX-2400.
DTR Data Terminal Ready - Input to Modem - Asserted (TTL low) 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 Modem - Asserted (TTL low) 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 Modem - A “handshaking” signal which is
asserted by the DTE (TTL low) 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 Modem - A “handshaking” signal which is
asserted by the DCE (TTL low) 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 RX and TX 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 RX line, and receives on TX.
“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.