ELM627

Elm Electronics – Circuits for the Hobbyist

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Pin Descriptions

Ordering Information

These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface

mount type of package. To order, add the appropriate suffix to the part number:

300 mil Plastic DIP............................... ELM627P

200 mil SOIC..................................... ELM627SM

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All rights reserved. Copyright ©1998 Elm Electronics.

Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be

given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information

described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these

products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or

systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve

reliability, function, or design.

This pin is the positive supply pin, and should

always be the most positive point in the circuit.

Internal circuitry connected to this pin is used to

provide power on reset of the microprocessor, so

an external reset signal is not required. Refer to

the Electrical Characteristics section for further

information.

Q (pin 2)

This signal is driven to a logical high level when a

break signal is detected, and during powerup.

Q (pin 3)

This output signal is normally held at a high level,

and is driven low when a break signal is detected,

as well as immediately after powerup.

P/C (pin 4)

This is the pulse/continuous control input pin,

used to modify the behavior of the circuit output.

If at a logic high when a break signal is detected,

the output will consist of a single 100ms pulse.

Otherwise,

the

output

will

remain

active

continuously until pin 5 returns to a logical low

level. The output duration will always be a

minimum of 10ms, and is 100ms on powerup.

TxD (pin 5)

This is the monitored signal input, usually

connected directly to the RS232 Transmit Data

line through a suitable current limiting resistor.

This input employs Schmitt trigger logic so that

input

waveshaping

circuitry

is

not

normally

required.

T1 (pin 6) and T0 (pin 7)

These are the threshold setting inputs. Logic

levels on these pins at the rising edge of TxD are

used to determine the required minimum duration

of the break signal, as shown in Table 1 below.

Circuit common is connected to this pin. This is

the most negative point in the circuit.

ELM627DSA

Threshold Setting

Min Break Signal

Baud rate, ‘00’ character sent

will trigger at

but not at

T1

T0

(msec)

L

L

L

H

L

H

H

H

5.0

11

22

120

1200

2400

600

1200

300

600

-

110

Table 1. Threshold Settings