ELM621 查看數據表（PDF） - Elm Electronics
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ELM621 Datasheet PDF : 6 Pages
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ELM621
Pin Descriptions
VDD (pin 1)
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.
B1 (pin 3), B2 (pin 2) and B3 (pin 7)
These are the three port pins that are software
configurable. At power-up, and after resetting,
these pins are inputs but can be individually set
as either input or output. The B3 pin has an
internal (nominally 30KΩ) pullup resistor that can
be enabled or disabled as required.
reset (pin 4)
This pin can be used to reset the circuit by
applying a momentary logic low level to it. If
unused, this pin should be left open (as a pullup
resistor is provided) or connected to VDD.
Rx (pin 5)
This is the RS232 receive input. Internal inversion
of the logic level allows the pin to be directly
connected to the DTE’s TxD line through a single
current limiting resistor (typically about 47KΩ).
Precautions should be taken in the circuit design
to allow for the possibility that this input may be
left floating, due to a disconnected serial cable.
Typically, this only requires a large-valued
resistor between the RS232 TxD pin and Vss.
Tx (pin 6)
The RS232 data output pin. Signal level is
compatible with most inverting interface ICs, and
drive is sufficient to allow interfacing using only a
single PNP transistor. See the Example
Application section for more details.
VSS (pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
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............................... ELM621P
200 mil SOIC..................................... ELM621SM
All rights reserved. Copyright ©1999 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.
ELM621DSA
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