Application Information

9-Pin SERIAL PORT APPLICATION

In a typical Data Terminal Equipment (DTE) to Data

Circuit-Terminating Equipment (DCE) 9-pin de-facto inter-

face implementation, 2 data lines and 6 control lines are re-

quired. The data lines are TXD and RXD and the control

lines are RTS, DTR, DSR, DCD, CTS and RI. The

DS14C335 is a 3 x 5 Driver/Receiver and offers a single chip

solution for the DTE interface as shown in

Figure 9.

Ring Indicator (RI) is used to inform the DTE that an incom-

ing call is coming from a remote DCE. When the DS14C335

is in SHUTDOWN (SD) mode, receiver five (R5) remains ac-

tive and monitors RI circuit. This active receiver (R5) alerts

the DTE to switch the DS14C335 from SHUTDOWN to ac-

tive mode.

MOUSE DRIVING

The DS14C335 was tested for drive current under the follow-

ing mouse driving conditions:

•

Two driver outputs set at V

together (paralleled), sourcing current to supply the V+

terminal of the mouse electronics

•

One driver output set at V

V− terminal of the mouse electronics

•

One receiver was used to accept data from the mouse

•

Power Supply Voltage (V

Completion of the testing (performed by National’s Data

Transmission Applications Group and a major PC manufac-

turer) concluded that the DS14C335 and it’s DC-DC Conver-

tor supplied adequate drive capability to power a typical PC

mouse. The mouse tested was specified with the following

conditions:

10 mA at +6V

5.0 mA at −6V

Since driver current is limited, it is recommended that newer

lower power mice be specified for battery powered applica-

tions. Using older high power mice is wasteful of precious

battery charge.

EXTERNAL DC-DC CONVERTOR COMPONENTS

The DS14C335 with it’s unique DC-DC Convertor triples the

power supply voltage (3.0V) to +9.3V and then inverts it to a

−9V potential. This unique convertor ONLY requires 5 exter-

nal surface mount 0.47 µF capacitors. The five identical

components were chosen to simplify PCB layout and the

procurement of components. The DS14C335’s DC-DC Con-

vertor also provides a larger signal swing (higher at RS-232

standard data rates) which translates to more noise margin

for the rejection of ground potential differences, induced

noise, and crosstalk compared to other DC-DC convertor

schemes which only provide limited signal swing and limited

noise margin.

DC-DC CONVERTOR CAPACITORS

The use of polarized capacitors is not required. However, if

they are used, the polarity indicated in the DS14C335 Func-

tional Diagram must be honored for proper operation. Sur-

face mount capacitors or ceramic capacitors may be used,

however, for optimal efficiency, capacitors with a low effec-

tive series resistance (ESR) should be used. Values in the

low Ohms(

Ω) is normally acceptable.

INTEROPERATION WITH +5V UARTs

The DS14C335 provides full RS-232 driver output levels and

a single chip solution for the popular 9-pin defacto serial port.

This device may be used in either pure +3V applications or

DS011734-11

FIGURE 9. Typical DTE Application

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