IP920 Operating Manual: A Serial Interface 51
A. 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 IP920 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 IP920.
RX
Receive Data - Output from Modem - Signals transferred from the
IP920 are received by the DTE via RX.
TX
Transmit Data - Input to Modem - Signals are transmitted from the
DTE via TX to the IP920.
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.
To Next Page
Loading...