ELM621
Serial Three Bit Port
Description
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.
Features
• 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
Connection Diagram
PDIP and SOIC
(top view)
V
DD
B2
B1
reset
1
2
3
4
8
7
6
5
V
SS
B3
Tx
Rx
Applications
• Home automation monitoring and control
• Robotics
• Security monitoring
• IC programmers
V
DD
Block Diagram
Tx
Rx
6
RS232
Interface
V
DD
reset
4
Command
Interpreter
7
B3
B2
B1
5
Port
Control
2
3
ELM621DSA
Elm Electronics – Circuits for the Hobbyist
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