ELM ELM624SM, ELM624P Datasheet

ELM624

Control L to RS232 Interpreter

Description

1238765

4

5

2

3

4

6

7

Features

The Control L or LANC interface is an industry
standard for many audio and video devices. It uses a
bit serial format that is similar to RS232, but differs
enough that devices cannot be directly connected to
one another. The ELM624 provides the necessary
logic to allow almost transparent transfer between
the two systems.

In operation, commands are sent to the ELM624
using an RS232 serial connection, translated to the
Control L format, and sent to the controlled device
on the LANC port. The resulting responses are then
converted to a series of ASCII characters and
transmitted back to the controlling serial device.

This integrated circuit was designed to provide a
cost-effective way for experimenters to work with the
Control L system, so many features typically found in
commercial devices, such as RS232 handshaking,
variable baud rates, extra buffering of signals, etc.
have not been implemented. Responses are kept to
a minimum as well (eg. a single question mark is
returned for a misunderstood command), but the
general principles are demonstrated, and for many
applications, this is all that is required.

Applications

• Video editors

• Low power CMOS design

• High speed RS232 communications

• Configurable with standard AT commands

• ASCII output formatted as standard hex digits

• Minimum of external components required

• Most Control L formats supported

• External reset input for system use

• Crystal controlled for signal accuracy

Connection Diagram

PDIP and SOIC

(top view)

VDD VSS
XT1
XT2

reset Rx

LANC
Tx

• Time-lapse recording controllers

• Remote camera controls

• Computer control of A/V equipment

Block Diagram

XT1

3.58MHz

XT2

reset

ELM624DSB

Master

Oscillator

VDD

Control L

Interface

Control

RS232

Interface

Elm Electronics – Circuits for the Hobbyist

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

VDD

LANC

VSS

Tx

Rx

1 of 7

ELM624

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.

XT1 (pin 2) and XT2 (pin 3)

A 3.579545MHz NTSC television colourburst

crystal is connected between these two pins.
Crystal loading capacitors (typically 27pF) will
also normally be connected between each of the
pins and Vss.

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 either be connected to
VDD, or left open (as an internal pullup resistor is
provided).

Rx (pin5)

The computer’s RS232 transmit signal is directly

connected to this pin through a single current
limiting resistor (typically about 47KΩ). Internal
signal inversion and Schmitt trigger waveshaping
provide the necessary signal conditioning.

Tx (pin 6)

The RS232 data output pin. Signal level is
compatible with most interface ICs, and drive is
sufficient to allow interfacing using only a single
PNP transistor if desired. See the Example
Application section for more details.

LANC (pin 7)

This is the open drain Control L (LANC) interface
pin. An internal pullup resistor is provided for a
nominal drain load.

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............................... ELM624P 200 mil SOIC.....................................ELM624SM

All rights reserved. Copyright ©1999 & 2000 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.

ELM624DSB

Elm Electronics – Circuits for the Hobbyist

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

2 of 7

ELM624

Absolute Maximum Ratings

Storage Temperature.......................-65°C to +150°C

Ambient Temperature with

Power Applied....................................-40°C to +85°C

Note:
Stresses beyond those listed here will likely damage

the device. These values are given as a design
guideline only. The ability to operate to these levels

Voltage on VDD with respect to VSS............0 to +7.5V

is neither inferred nor recommended.

Voltage on any other pin with

respect to VSS........................... -0.6V to (VDD + 0.6V)

Electrical Characteristics

All values are for operation at 25°C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.

Characteristic Minimum Typical Maximum ConditionsUnits

Supply Voltage, VDD 4.5 5.0 5.5 V

VDD rate of rise 0.05 V/ms

Average Supply Current, IDD 1.0 2.4 mA

Input low voltage VSS 0.15 VDD V

Input high voltage VDD V0.85 VDD

see note 2

see note 3

Output low voltage 0.6 V

Output high voltage VVDD - 0.7

Internal pullup resistances
(see note 4)

Rx pin input current

RS232 Baud Rate

-0.5

500 KΩ300 600

+0.5

9600

Notes:

1. This integrated circuit is produced with a Microchip Technology Inc.’s PIC12C5XX as the core embedded
microcontroller. For further device specifications, and possibly clarification of those given, please refer to the
appropriate Microchip documentation.

2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved
using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as
may be obtained through direct connection to solar cells, or some charge pump circuits.

3. Device only. Does not include any load currents.

4. The value of the internal pullup resistance is both supply and temperature dependent.

5. This specification represents the current flowing through the protection diodes when applying large voltages
to the Rx input (pin 5) through a current limiting resistance. Currents quoted are the maximum continuous.

6. Nominal data transfer rate. Assumes that a 3.58 MHz crystal is used as a frequency reference. Data is
transferred to and from the ELM624 with 8 data bits, no parity, and 1 stop bit (8 N 1).

KΩ3020 50

mA

baud

Current (sink) = 8.7mA

Current (source) = 5.4mA
Pin 4 (reset)

Pin 7 (LANC)

see note 5

see note 6

ELM624DSB

Elm Electronics – Circuits for the Hobbyist

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

3 of 7