Appendices; Appendix A: Serial Interface - Microhard Systems BulletPlus Operating Manual

Appendix A: Serial Interface

Module Host (e.g. PC)
(DCE)
Signal
1 DCD 
2 RX 
3  TX
4  DTR
5 SG
6 DSR 
7  RTS
8 CTS 
DCD Data Carrier Detect - Output from Module - When asserted (TTL low), DCD informs the DTE that a
communications link has been established with another device.
RX Receive Data - Output from Module - Signals transferred from the BulletPlus are received by the DTE via
RX.
TX Transmit Data - Input to Module - Signals are transmitted from the DTE via TX to the BulletPlus.
DTR Data Terminal Ready - Input to Module - Asserted (TTL low) by the DTE to inform the module 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 (TTL low) by the DCE to inform the DTE that it is alive
and ready for communications. DSR is the module's equivalent of the DTR signal.
RTS Request to Send - Input to Module - 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 Module - 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 module (DCE); the module transmits data on the RX line, and receives
on TX.
"DCE" and "module" are often synonymous since a module is typically a DCE device.
"DTE" is, in most applications, a device such as a host PC.
© Microhard Systems Inc.
(DTE)
Arrows denote the direction that signals are asserted (e.g., DCD originates at the
DCE, informing the DTE that a carrier is present).
IN
The interface conforms to standard RS-232 signals, so direct connection to a
IN
host PC (for example) is accommodated.
OUT
OUT
IN
OUT
The signals in the asynchronous serial interface are described below:
IN
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