SP503AN

SP503 Application Note

© Copyright 2000 Sipex Corporation

2

DTE and DCE configurations

with the SP503

The SP503 has designated signals such as "Trans-

mit Data", "Clear-to-Send", etc.which design-

ers can easily allocate the appropriate SP503

transceivers for the corresponding signals. The

data signals specified in the EIA standards and

CCITT are referenced in the SP503 datasheet as

DTE. Some customers have wondered if they

can use the SP503 for DCE applications.

Although it can be confusing at first glance, the

DCE implementation is the mirror image of the

DTE side. For the DTE, TxD is a driver which

drives the data to RxD, a receiver, on the DCE

side. TxC or TT is a driver on the DTE side

which drives the clock signal to the RxC re-

ceiver on the DCE side.

The next three pages illustrate the CCITT signal

allocations from the SP503 in either DTE or

DCE to the DB-25 connector. As shown, it is

possible to use a DB-25 connector for the vari-

ous protocols offered by the SP503.

DB-25 Connector Pin Assignments for Various Protocols

DB-25 Pin #

RS-232

EIA-530

RS-449

RS-422

V.35

V.36

1

shield

shield

shield

shield

CCITT# 101 CCITT# 101

2

TxD

TxD(A)

SD(A)

T(A)

103(A)

103(A)

3

RxD

RxD(A)

RD(A)

R(A)

104(A)

104(A)

4

RTS

RTS(A)

RS(A)

C(A)

105

105(A)

5

CTS

CTS(A)

CS(A)

–

106

106(A)

6

DSR

DSR(A)

DM(A)

–

107

107(A)

7

Signal GND

Signal GND

Signal GND

Signal GND

102

102

8

DCD

RLSD(A)

RR(A)

I(A)

109

109(A)

9

–

RxC(B)

RT(B)

–

115(B)

115(B)

10

–

RLSD(B)

RR(B)

I(B)`

–

109(B)

11

–

TxC(B-DTE)

TT(B)

–

113(B)

113(B)

12

DCD (2nd)

TxCC(B-DCE)

ST(B)

S(B)

114(B)

114(B)

13

CTS (2nd)

CTS(B)

CS(B)

–

–

106(B)

14

TxD (2nd)

TxD(B)

SD(B)

T(B)

103(B)

103(B)

15

TxCC (DCE) TxCC(A-DCE)

ST(A)

S(A)

114(B)

114(B)

16

RxD (2nd)

RxD(B)

RD(B)

R(B)

104(B)

104(B)

17

RxC

RxC(A)

RT(A)

–

115(A)

115(A)

18

LL

LL

LL

–

–

141

19

RTS (2nd)

RTS(B)

RS(B)

C(B)

–

105(B)

20

DTR

DTR(A)

TR(A)

–

–

–

21

RL

RL

RL

–

–

140

22

RI

DSR(B)

DM(B)

–

–

107(B)

23

SRS

DTR(B)

TR(B)

–

–

–

24

TxC (DTE)

TxC(A-DTE)

TT(A)

–

113(A)

113(A)