ELM622

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............................... ELM622P

200 mil SOIC..................................... ELM622SM

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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.

Tx (pin 2)

The transmit data output. When a valid byte is

received it is retransmitted from this pin at 9600

baud, least significant bit first, with one start bit,

no parity bit, and one stop bit. The pin is normally

held at a logic high level when in the idle state,

and goes to true logic levels when transmitting

data. The output is compatible with standard

RS232 data transmission, when coupled through

appropriate buffers (transistors or interface ICs

such as the MAX232).

RTS (pin 3)

RTS is the request to send handshaking output.

When a valid byte is ready to be sent, this pin will

be brought low and will remain at that level until

the stop bit has been sent, or the send is aborted

due to a time-out.

CTS (pin 4)

This input pin is used to control the transmission

of data. A logic low level allows sending, and a

high level forces the ELM622 to wait. The system

waits no longer than about 2 seconds, however,

before discarding the byte and reverting to the

idle condition. The state of the pin is tested just

prior to sending data, and is not monitored once

data transmission begins.

IRRx (pin 5)

The output of a standard 40KHz infrared receiver

module is connected to this pin, through a series

resistor of about 5K

Ω value. The output of such a

module is normally at a high level, and switches

to a logic low when modulated carrier is received.

LED (pin 6)

This pin provides a logic high level output when a

valid code has been received and remains at that

level until the data has been sent by the ELM622.

The output is suitable for driving an LED through

a current limiting resistor.

Reset (pin 7)

A high level 100msec wide pulse is output on this

pin when the sequence 99999 is received. This

can be used for special functions such as

resetting the system, or momentarily triggering a

control point.

Circuit common is connected to this pin. This is

the most negative point in the circuit.

ELM622DSA