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ELM621

ELM621DSA

Elm Electronics – Circuits for the Hobbyist

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

The following lists the commands that the

ELM621 recognizes. These are collectively referred

to as ‘AT’ commands due to the fact that each line

must be preceeded by the letters ‘A’ and ‘T’.

All commands except reset (‘Z’) require two

characters to be complete. The first is a descriptive

letter, while the second is chosen from one of the

options shown within the square brackets, adjacent

to the letter.

As an example, the R or read command can be

followed by either a 1, 2, 3, or an A, so to read the

state of bit 2, the command ‘AT R2’ would be issued,

and AT RA will read all bits.

AT Commands

Device Control

E [ 1 | N ] - terminal echo on

Selecting either E1 or EN will cause all characters

sent to the ELM621 to be retransmitted (or echoed)

back to the controlling device.

E [ 0 | F ] - terminal echo off

Selecting either E0 or EF will stop the echoing of

characters back to the controlling device.

ID - show the device identification string

This command is used to display the type of device

connected and the ROM version.

Z - reset

This command is used to reset the ELM621 to the

power on state. All three port pins will be configured

as inputs, the pullup resistor will be off, the output

latches will be cleared, and terminal echo will be

on.

Port Control

I [ 1 | 2 | 3 | A ] - set port bit to input

Individually selects one, or simultaneously selects

all pins to be inputs, turning off the respective

output driver if it were on.

O [ 1 | 2 | 3 | A ] - set port bit to output

Selects one or all pins to be outputs, enabling the

respective output drivers. If the pullup were on, and

O3 or OA were issued, then the pullup would be

temporarily disabled. Returning B3 to the input

state would restore the pullup resistance.

P [ 1 | N ] - turn the B3 pullup resistance on

Selecting either P1 or PN will enable the internal

30K

P [ 0 | F ] - turn the B3 pullup resistance off

Selecting either P0 or PF will disable the internal

30K

Bit Control

C [ 1 | 2 | 3 | A ] - clear the output bit

of the port bits. If the pin(s) are also selected to be

outputs, then the logic level will appear immediately

on the output.

S [ 1 | 2 | 3 | A ] - set the output bit

of the port bits. If the pin(s) are also selected to be

outputs, then the logic level will appear immediately

on the output.

T [ 1 | 2 | 3 | A ] - toggle the state of the output bit

Reverses (or toggles) the logic level of the selected

pin(s). As with C or S, the pin(s) must also be

selected as outputs for an external change to occur.

The toggle command is convenient for creating

pulses, or strobes, on pins. For example, if bit 3 is

configured as an output, and is at a low level,

issuing the command AT T3 T3 will cause pin 7

(B3) to momentarily go to a high level, then return

low. As the ELM621 is interpreter driven, the width

of the pulse will be related to the number of

characters that need be translated. Minimum width

(~60µsec) is obtained with ATT3T3.

R [ 1 | 2 | 3 | A ] - read the level of the port pin

Reads the voltage level at the selected pin(s) and

reports the measured logic level. For example, if pin

in a response of B2=1.