Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 43)

Chapter
Using the Communication Ports 2
2 -5
Hardware Handshaking
The BASIC module uses these rules when hardware handshaking is
enabled. The BASIC module:
does not transmit until CTS, DCD, and DSR become active
examines DSR and DCD following the receipt of a character. If the
DSR and DCD are active, the character is placed in the input queue.
If DSR or DCD is inactive, the character is assumed to be noise and is
discarded.
Important: You need to know whether the device connecting to the
BASIC module has a DTE or DCE interface.
The BASIC module serial ports are configured as 25-pin Data Terminal
Equipment (DTE), as are most terminals or computer ports.
DTE 25 pinout Signal description Signal from DTE perspective DTE 9 pinout Signal description
2 TXD–Transmitted Data Output 3
3 RXD–Received Data Input 2
4 RTS–Request to Send Output 7
5 CTS–Clear to Send Input 8
6 DSR–Data Set Ready Input 6
7 Com–Signal Common Shared 5
8 DCD–Data Carrier Detect Input 1 CD–Carrier Detect
20 DTR–Data Terminal Ready Output 4
22 NC–No Connection
(for BASIC module only) Input 9 RI–Ring Indicator (BASIC
module does not support)
Devices such as modems are Data Communication Equipment (DCE).
Pinouts on these terminals are defined for ease of interfacing with DTE
equipment.
DCE 25 pinout Signal description Signal from DC perspective DCE 9 pinout
2 TXD–Transmitted Data Input 3
3 RXD–Received Data Output 2
4 RTS–Request to Send Input 7
5 CTS–Clear to Send Output 8
6 DSR–Data Set Ready Output 6
7 Com–Signal Common Shared 5
8 CD–Carrier Detect Output 1
20 DTR–Data Terminal Ready Input 4
22 RI–Ring Indicator Output 9
Important: All signal directions that are listed in the previous two tables
are valid. For example, TXD, Transmitted Data, is a DTE output but is
also a DCE input. The signal description is the same for both the DTE and
DCE but the direction of the signal (perspective) has changed based on
whether you have a DTE
or DCE device.