SP503AN

SP503 Application Note

Due to its flexibility and programmability,
the SP503 has been finding its way into
many new networking products. The SP503
offers an excellent replacement for discrete
solutions on X.25 implementations for frame
relay systems, multi-protocol routers and
other WAN products where many designs
run various modes such as RS-232,
RS-422, V.35 or V.36.

For RS-232, the older bipolar 1488 and
1489 parts, or even the newer MAX230 or
SP230 series have traditionally been used.
For RS-422 or RS-485, the 26LS31,
26LS32, 3488, and 3489 have been seen in
many designs. These parts have been also

used for V.35 but with external termination
resistors. For a typical design, four RS-232
chips would be used for a complete
RS-232 port, four RS-422 chips for an
RS-422 port and four chips for V.35 with an
external resistor network. Port programma-
bility would require relays or switches so
that software lines can control whether
RS-232 is active or RS-422 is active. The
relays increase board capacity as well as
cost to the design.

The SP503 solves board space and cost
problems by offering a single packaged part
that supports various protocols and also
offers software programmability to the port.

DTE and DCE configurations with
the SP503

Connecting the SP503 to a DB-25
connector in DTE and DCE modes

Implementing V.35 with the SP503

Creating extra single-ended and
differential channels with the SP503
using the SP310A and SP485

Using external supplies with the SP503

SP503

Application Note

Typical discrete solution vs. the SP503

SP503AN

SP503 Application Note

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

shield

CCITT# 101 CCITT# 101

TxD

TxD(A)

SD(A)

T(A)

103(A)

RxD

RxD(A)

RD(A)

R(A)

104(A)

RTS

RTS(A)

RS(A)

C(A)

105

105(A)

CTS

CTS(A)

CS(A)

106

106(A)

DSR

DSR(A)

DM(A)

107

107(A)

Signal GND

102

DCD

RLSD(A)

RR(A)

I(A)

109

109(A)

RxC(B)

RT(B)

115(B)

RLSD(B)

RR(B)

I(B)`

109(B)

TxC(B-DTE)

TT(B)

113(B)

DCD (2nd)

TxCC(B-DCE)

ST(B)

S(B)

114(B)

CTS (2nd)

CTS(B)

CS(B)

106(B)

TxD (2nd)

TxD(B)

SD(B)

T(B)

103(B)

TxCC (DCE) TxCC(A-DCE)

ST(A)

S(A)

114(B)

RxD (2nd)

RxD(B)

RD(B)

R(B)

104(B)

RxC

RxC(A)

RT(A)

115(A)

141

RTS (2nd)

RTS(B)

RS(B)

C(B)

105(B)

DTR

DTR(A)

TR(A)

140

DSR(B)

DM(B)

107(B)

SRS

DTR(B)

TR(B)

TxC (DTE)

TxC(A-DTE)

TT(A)

113(A)

SP503AN

SP503 Application Note

DTE-DCE flexibility with the SP503 on a DB-25 serial port

DB-25
Connector

TxD

TxC

DTR

RTS

RxD

RxC

CTS

DCD

TxD
TxC

DTR
RTS

RxD
RxC
CTS

DCD

RDEC0

RDEC1
RDEC2
RDEC3
TDEC0
TDEC1

TDEC2
TDEC3

2 3

5 12 11 10 9

2 3 4 5 12 11 10 9

14
15

20
80

DSR
RI
SCT

24
17

Quad 2:1 Mux

1B
2A
2B
3A
3B
4A
4B

SEL

"0" = DTE
"1" = DCE

SCC

SD(A)
SD(B)

TT(A)
TT(B)
TR(A)

TR(B)
RS(A)
RS(B)

RT(A)

RT(B)

RD(A)

RD(B)

CS(A)
CS(B)

RR(A)

RR(B)

DM(A)
DM(B)

SCT(A)

SCT(B)

IC(A)
IC(B)

LL(A)

LL(B)

ST(A)
ST(B)

SP503
DTE
Config.

SP503
DCE
Config.

59
63

65
58
56

54
52
70

37
38

66
67
35
36

69
76

77
39

51
49

42
44

61
59

63
65
58

56
54

70
71

38
66

67
35
36
68

69
76

77
39
40

51
49
42
44

RL(A)

15
12

TxD

TxC

DTR

RTS

RxD

RxC
CTS

DCD

20
80
19

DSR
RI
SCT

RL
ST

79
24
17

SD(A)

SD(B)

TT(A)
TT(B)

TR(A)
TR(B)
RS(A)

RS(B)

RT(A)

RT(B)

RD(A)
RD(B)

CS(A)

CS(B)
RR(A)
RR(B)

DM(A)
DM(B)

SCT(A)
SCT(B)

IC(A)
IC(B)

LL(A)

ST(A)

ST(B)
RL(A)

LL(B)

SP503AN

SP503 Application Note

SP503 V.35 External Termination
Resistors

V.35 implementation requires external resistors
to be connected to the driver outputs and re-
ceiver inputs. The resistors are needed for
reducing signal levels and maintaining input
and output impedance levels that conform to
CCITT Recommendation V.35. The drawings
below offer both receiver input termination and
driver output termination configurations that
will comply to V.35.

As you may know, the termination resistors are
for V.35 mode only and have to be disconnected
when another mode is programmed. There are
a few ways to connect and disconnect the net-
work. One method is to add a daughter-card
option slot onto the main printed circuit board
where the SP503 is mounted. This allows the
user to add a mini-PC card that contains the V.35

network to be connected to the driver outputs
and receiver inputs. Another method is to
implant the V.35 network into a cable if the user
requires conversion cables to switch from one
protocol to another. For example, if the serial
port has a DB-25 connector and requires an
ISO-2593 connector for V.35; a DB-25 to
ISO-2593 conversion cable containing the V.35
network is connected to the port.

Of course this method will not allow program-
mability to the serial port if the user wants to run
various protocols to that port. To actively switch
protocols by software control, you can use ana-
log switches or relays. Sipex recommends us-
ing low-ON resistance analog switches, such as
Siliconix DG643

analog switches for the driver

outputs, and solid-state relays such as the AT&T
LH1514

for the receiver inputs. See opposite

page for an example of the SP503 V.35 configu-
ration. For other termination networks, please
consult the factory.

120

SOURCE

= 97

= 148

[90

to 110

]

[135

to 165

]

232

200

107

100

LOAD

-5V

SOURCE

= 96

= 154

[50

to 150

]

[135

to 165

]

= 0.55V

DC_OFF

= 0.0V

[+0.44V to +0.66V]

[-0.6V to +0.6V]

Typical values

V.35 Receiver Input Termination Resistor Network

V.35 Driver Output Termination Resistor Network

SP503AN

SP503 Application Note

SP503 Switching Configuration for V.35 Implementations

· Switches are Siliconix DG643DY analog switches.

· Solid-State Relays are AT&T, LH1514.

· Resistors are 1/8W, 1% tolerance.
· External Supplies necessary are: V

= +5V, V+ = +12V (for V+ on the DG643DY) and V

= -5V.

Receivers

TxD

Drivers

DTR

RTS

TxC

SP503CF

RxD

RxC

CTS

DSR

DCD

SCT

V+

V-

+5V

Driver Outputs & Receiver Inputs
are in DTE mode.

to pin 12 of the 74LS11

74LS11

74LS11 (3-Input AND Gate)

RxC (115)

RxD (104)

TxD (103)

TT (113)

TxCC (114)

to pin 6 of the 74LS11

74LS11

LH1514

74LS11

LH1514

7
5

LH1514

+12V

120

3
7

10 14

1
16

V+

V-

V+

DG643

200

232

-5V

107

V-

to V-

+12V

3
7

10 14

1
16

V+

V-

V+

DG643

+12V

200

232

-5V

107

V-

3
7

10 14

1
16

V+

V-

V+

DG643

+12V

200

232

-5V

107

+5V

1/4
74LS11

+5V

RDEC1 & TDEC1

RDEC2 & TDEC2

RDEC3 & TDEC3

(pins 3 & 11)

(pins 4 & 10)

(pins 5 & 9)

to pin 6 of the 74LS11

74LS11

1/4
74LS11

SP503AN

SP503 Application Note

Typical Applications Questions
on the SP503

Can the SP503 be used with external power
supplies? If so, is there a power-up sequence?
The internal charge pump can be bypassed
through external supplies to V

and V

. The

external voltage should be +10V for V

and

-10V for V

. The tolerance is

5%. The

absolute minimum limit for the external supplies
is

7V and the absolute maximum limit is

10.5V.

The SP503 does require a power-up sequence of
+10V, +5V, -10V for proper operation. Addi-
tional external circuitry will be required for the
correct sequencing. Consult factory for details.

What is the maximum input voltage applied to
the receiver input without damaging the SP503?
The receiver inputs can tolerate up to

16V in

any protocol without latching up the device.
Since RS-232 ranges from

5V to

15V; the

SP503 is well within the accepted range. It may
be worthwhile to include 15V clamping diodes
or transient voltage suppressors so that the re-
ceiver input will be held below

15V.

What is the maximum short-circuit voltage that
can be applied to a SP503 driver output?
The driver outputs can be shorted up to

16.0V

without causing damage to the driver. Between
the

16V range, the SP503 adheres to the RS-

232 short circuit current limit of 100mA and to
the RS-422/RS-423 limit at 150mA. Again,
transient voltage suppressors or clamping diodes
will protect the SP503 if exceeding the

16V

range is possible.

What is the state of the SP503 drivers and
receivers when the device is addressed with
0000?
The SP503 drivers are in a high impedance(over
1M

) tri-state condition when "0000" is ad-

dressed. The receivers are not tri-stated and the
outputs are undefined. This means that they
could be floating to either a high or low level
depending on the previous state of the receiver
input prior to the 0000 addressing change. The
receiver input impedance is at 15k

for "0000".

Can the SP503 be programmed for 7 drivers and
7 receivers in RS-423 mode?

The SP503 can be switched to RS-423 mode by
programming TDEC

, TDEC

to "1000" for the drivers and RDEC

to "1000"

for the receivers. However, external supplies
must be used in order to drive RS-423. The
internal charge pump can only support up to
three RS-423 drivers and three RS-423
receivers.

What is the power dissipation in the SP503 and
in which mode does it consume the most power?
The SP503 dissipates approximately 400mW to
1.4W depending on the protocol. RS-485 mode
consumes the most power at 1.4W. For worst
case power dissipation, all seven drivers were
driven with a TTL signal and the outputs were
looped back into the receiver inputs to generate
a TTL output. All drivers and receivers were
active.

MODE

RS-232

0.418W

RS-422

0.970W

RS-485

1.382W

RS-449

0.959W

EIA-530

0.959W

V.35

1.055W

What is the state of the SP503 drivers and
receivers when the device is addressed with
1111?
The address for "1111" is not used in the SP503.
If the SP503 is programmed for "1111", the
drivers are approximately 1.0V and at a high
impedance (approx. 9M

). The receivers are

not tri-stated and the outputs are undefined. All
receiver inputs are at 15k

input impedance.

The SP503 can receive a "1111" address while
V

is off. The supply current is approximately

50mA (V

= +5V) while the address is at

"1111".

In the RS-232 signal assignments for the DB-25
connector, where does the SP503 account for
Test Mode (TM) ?
For most RS-232 applications, the signals com-
monly used are TxD, TxC, RxD, RxC, RTS,
CTS, DSR, SG, DCD, DTR and Frame Ground.

SP503AN

SP503 Application Note

In DTE mode; TxD, TxC, RTS, DTR are the
drivers and RxD, RxC, CTS, DSR, DCD are the
receivers. Since there are seven drivers and
seven receivers in the SP503, the designer can
easily use the SP503 for the above signals. Other
RS-232 applications will support diagnostic func-
tions such as LL (driver), RL (driver), and TM
(receiver) which may or may not require extra
transceivers depending if other signals are not
used. Since Test Mode (TM) is a receiver for
DTE designs, the Ring Indicator (RI) receiver in
the SP503 (pin 21) can be used for TM if RI is not
used. If all the available drivers and receivers are
used in the SP503, then another RS-232 trans-
ceiver can be added. See page 230 and 231 for
suggestions on adding Sipex's RS-232 and
RS-485 transceivers.

Are the Schottky diodes used from Vcc to Vss
and from Vdd to C2- in the SP502 necessary for
the SP503?
Sipex has incorporated the Schottky diodes
(needed with the SP502) into the SP503 in order
to protect against potential start up problems due
to fast rate of rise on V

(

1V/

s) and overvolt-

age to the TTL inputs. However, a negative
voltage (V

-5V) applied to the receiver inputs

while the SP503 is powered off will cause start-
up problems to the charge pump. In order to
guard against this condition, an external Schottky
diode should be placed from V

to V

minimize V

current injection into the IC sub-

strate and allow the charge pump to operate
properly. See page 203 Figure 6 - Typical
Operating Circuit, for diode connection
schematic.

Can the SP503 be configured for V.36?
CCITT Recommendation V.36 is similar to RS-
449 where certain signals are RS-422 signals and
others are RS-423. Depending on different ap-
plications; "Transmit Data", "Terminal Timing",
"Request-to-Send", "Data Terminal Ready",
"Receive Data", "Transmit Clock", "Receive
Clock", "Clear-to-Send", "Data Carrier Detect",
and "DataSet Ready" are specified as Category 1
Circuits where the protocol is RS-422 for rates
over 20kbps. All other circuits are Category 2
Circuits which are specified as RS-423 circuits.
Depending on particular signals, the SP503 can
be easily used for V.36.

When the two drivers, ST and TT, are in tri-state
mode, what will the driver outputs tolerate for
maximum short circuit voltages? And the re-
ceiver, SCT, input?
The driver outputs will tolerate up to

16.0V

without any damage to the circuit regardless of
whether or not ST and TT are in tri-state mode.
The tri-state circuitry does not affect the short
circuit protection on the driver outputs. The SCT
receiver input will tolerate up to

16.0V without

any damage to the input structure regardless of
whether or not SCT is in tri-state mode.

What does Sipex recommend for transient volt-
age suppression techniques for the SP503?
For our evaluation boards, Sipex uses transient
voltage suppressor ICs from ProTek Devices,
model numbers LCA05C to LCA15C. The two
digits in the part number pertain to the rated
stand-off voltage, V

, which is the maximum

working DC voltage applied to the device. These
TVS devices are especially designed for serial
data communications because of their low ca-
pacitance and low impedance. However, please
be aware that V

values below the specified

input range of the transceiver will affect the input
impedance. For example, it would be fine to use
a 5V V

value for RS-422 but for RS-232, the

receiver input voltage range is

15V where lower

voltages will drive the impedance to ground.

Another recommended manufacturer is AVX
Corporation TransGuard series of TVS compo-
nents. AVX offers a variety of surface mount
back-to-back diodes.

ProTek Devices · P.O. Box 3129 · Tempe, AZ. 85280
· 602-431-8101
AVX Corporation · Myrtle Beach, SC · 803-448-9411

The drawing on page 232 shows the SP503
configured with the ProTek SM16LC15C TVS
devices to protect the drivers and receivers from
ESD and over-voltage.

Will the SP503 conform to the physical layer
testing specified by NET1/NET2 for X.21 and
X.25 systems?
Sipex initiated a component level test for NET1/
NET2 for V.28, V.10, V.11, V.35 protocols. The
SP503 passed all the physical layer testing re-
quirements prescribed by NET1/NET2. A full
test report can be furnished upon request.

SP503AN

SP503 Application Note

Creating extra RS-232 channels using the SP310A

1N5819

C1-

C2- V

C1+

C2+

+5V

SP503CF

Drivers

TxD

DTR

RTS

TxC

RxD

RxC

CTS

DSR

DCD

SCT

Receivers

+5V

V+

SP310ACT

RDEC

DB-25 connector in

DTE configuration.

C1-

C2- V

C1+

C2+

C1-

C2-

C1+

C2+

ON/OFF

V-

4 5

0.1

(Pin 3 of

the SP503)

SP503AN

SP503 Application Note

ORDERING INFORMATION

Model

Temperature Range

Package Types

SP503CF ............................................... 0

C to +70

C .................................................................. 80pin QFP

SP503EB ....................................................................................................................SP503 Evaluation Board

Corporation

SIGNAL PROCESSING EXCELLENCE

Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the
application or use of any product or circuit described hereing; neither does it convey any license under its patent rights nor the rights of others.

Sipex Corporation

Headquarters and
Sales Office
22 Linnell Circle
Billerica, MA 01821
TEL: (978) 667-8700
FAX: (978) 670-9001
e-mail: sales@sipex.com

Sales Office
233 South Hillview Drive
Milpitas, CA 95035
TEL: (408) 934-7500
FAX: (408) 935-7600

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