23

®

RS-232 P1 P

RS-232 P1 P

RS-232 P1 P

RS-232 P1 P

RS-232 P1 Pin Descriptions

in Descriptions

in Descriptions

in Descriptions

in Descriptions

RS-485 P2 P

RS-485 P2 P

RS-485 P2 P

RS-485 P2 P

RS-485 P2 Pin Descriptions

in Descriptions

in Descriptions

in Descriptions

in Descriptions

Pin 1

Case

Case Ground

Pin 1

12VAC

Pin 2

TD

Transmit Data

Pin 2

PWR RTN

Pin 3

RD

Receive Data

Pin 3

RTS A

Pin 4

RTS

Request To Send

Pin 4

RTS B

Pin 5

CTS

Clear To Send

Pin 5

CTS A'

Pin 6

DSR

Data Set Ready

Pin 6

CTS B'

(connected to Data

Pin 7

TD A

Terminal Ready)

Pin 8

TD B

Pin 7

Sig Gnd

Signal Ground

Pin 9

SIG RTN

Pin 8

RLSD

Receive Line Signal Detect Pin 10

RD A'

Pin 9

+12VDC

Positive DC Supply Input

Pin 11

RD B'

Pin 10

–12VDC

Negative DC Supply Input

Pin 12

SIG RTN

Pin 16

Echo Sup Echo Suppression

(tie to pin 17 to enable)

Pin 17

Echo Sup Echo Suppression

(tie to pin 16 to enable)

Pin 20

DTR

Data Terminal Ready

(connected to Data

Set Ready)

The LDM485 conforms to EIA RS-232 and RS-485 specifications.

Data Terminal Ready must be asserted by the host RS-232 port before

the LDM485 can transmit data. When Data Terminal Ready is not

asserted, all outputs of the LDM485 are high impedance, allowing up

to 64 LDM485 units to be multidropped on a common

communications cable. See Figures 1 and 3 for details.

Request To Send and Clear To Send are carried through the RS-485

port as two separate wire pairs. These may be used for full duplex

flow control.

Cable Capacitance Effects On Distances

The distances in the specifications are for the wire sizes 18-24AWG

For higher capacitance cables, decrease distance specifications for

Figure 1. LDM485 Logic Diagram

TD

RD

RTS

DTR

DSR

RLSD

CTS

+ 12VDC

Gnd

Case

RLSD

RD

DCE

DTE

TD

RTS

DTR

Light = High = Space

+V

CTS

* Light = High = Asserted

+V

+V

Light = Low = TD/RTS Enabled

Light = Low = Asserted

Light = Low = Space

+

-

+

-

8

7

4

3

B’

A’

RD

12VAC

PWR RTN

A’

B’

CTS

Opto-Iso

Barrier

+V

+V

+V

-12VDC

RTS

TD

SIG RTN

SIG RTN

(Isolated RS-485 Ground)

* "Light"is presence of light

across Opto-Iso barrier.

Echo Sup.

Echo Sup.

+5I

1k

120

1k

+5I

1k

120

1k

5

2

1

2

3

4

6

8

5

9

7

1

10

6

9

16

17

20

RS-232

P1

RS-485

P2

TD, RD

RTS, CTS, DTR, RLSD

Mark =-V; Space = +V

Asserted = + V, Not Asserted = -V

Mark

Space

Asserted

Not Asserted

Aor A’

Low

High

High

Low

BorB’

High

Low

Low

High

NOTE: Open or Tri-State on RD inputs produces

a Mark state, and on CTS inputs produces an

Asserted state.

TD, RD

RTS, CTS

11

12

10

B

A

B

A