ELM621

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Connection Diagram

PDIP and SOIC

(top view)

Serial Three Bit Port

The ELM621 is a serially controlled, three bit

parallel I/O port in an 8 pin package. The high level

of integration employed means that very few

external components are required in order to

construct a fully functional circuit with this IC.

The ELM621 offers several convenient features

that many users will appreciate. The provision of a

16 byte buffer allows commands to be chained and

executed sequentially with one key stroke. The

controllable pullup resistor on the bit 3 port pin is

particularly helpful when interfacing to mechanical

switches, while the ability to control character echo

reduces overhead while operating under computer

control. Naturally, individual as well as simultaneous

read, set, clear and toggle commands are also

supported.

All communications with this device are via a

standard 9600 baud RS232 connection, using AT

style commands. No special characters are required,

so that virtually any terminal program can be used

with the ELM621. More advanced users will be

interested in operating this device under computer

program control – simply a matter of writing to and

reading from the device.

• Low power CMOS design - typically 1mA

• High speed (9600 baud) RS232 communications

• Standard ASCII commands and responses

• 16 byte receive buffer

• Switchable pullup resistance

• Minimum of external components required

• External reset input

• High current drive outputs - up to 25 mA

• Home automation monitoring and control

• Robotics

• Security monitoring

• IC programmers

B3

Tx

Description

Applications

Block Diagram

1 of 6

Features

ELM621DSA

reset

Rx

1

2

3

8

7

6

5

4

B2

B1

Tx

RS232

Interface

Command

Interpreter

5

B1

B2

reset

4

6

7

Rx

B3

2

3

Port

Control