ELM627
RS232 Break Detector
Description
The ELM627 is a complete circuit for detecting
break signals on RS232 lines, in an 8 pin package.
This is useful for remotely resetting circuits through a
serial link. For convenience, this circuit also
generates an output pulse on power-up.
The timing threshold for break signal detection is
user selectable, allowing the circuit to respond to
transmitted null characters, <ctrl>@, at various baud
rates. This provides a convenient means for the
remote triggering of this circuit by simply shifting to a
lower baud rate and sending a null byte.
Two complementary high current outputs are
provided by the ELM627, so that further buffering is
not usually required. The output signal can be
selected to be either a continuous one (following the
TxD input line) or else a 100ms pulse output.
No external components are required for circuit
operation other than possibly a current limiting
resistor, as all timing references are generated
internally.
Features
• Low power CMOS design - typically 1mA at 5V
• No external timing elements required
• Complementary outputs
• Digitally controlled threshold timing
• Selectable output duration
• High current drive outputs - up to 25 mA
Connection Diagram
PDIP and SOIC
(top view)
V
DD
Q
Q
1
2
3
4
8
7
6
5
V
SS
T0
T1
TxD
Applications
• Remote resetting of RS232 devices
• Edge triggered one-shot circuits
• Digitally controlled sequencing schemes
• Watchdog type signal monitors
P/C
Block Diagram
Power on
Detect
TxD
5
Programmable
Timer
Output
Logic
2
Q
6
7
4
3
Q
T1
T0
P/C
ELM627DSA
Elm Electronics – Circuits for the Hobbyist
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