AS2702 – AS-Interface Slave IC

Revision 1.3, 21-Aug-08

Page 10 of 13

Operation Status Pins LED1 and LED2

Pins LED1 and LED2 are both equipped with a low-side open-drain output switch plus a passive high-side current source with a

nom. 10µA pull-up current capability. They will each have an LED load connected to UOUT, which will flag the operation status of

the slave device, according to the following table:

Output LED1

Output LED2

Flagging Priority

Slave Device

Reason

(green LED

connected)

(red LED

connected)

(1 = highest, …,

4 = lowest)

Operation Status

off

off

Supply voltage off

No supply voltage

on

off

Regular operation

off

of

4

No data communication

Regular, non-zero slave address

coded; data comm. watchdog

triggered

blinks

on

3

No regular slave address

coded

Slave address = default zero

blinks

blinks (alternating

with LED1)

2

Hardware failure in

sensor/actuator circuitry

Input PFAULT = L

off

blinks

1

External RESET or

overload at UOUT pin

DSTBn = L to RESET, or UOUT

switched-off due to overload

(LED1 and LED2 both also feature an input stage, to simplify component test and shorten test time of the slave device.)

The dc- and timing parameters of pins LED1 and LED2 are specified as follows:

Symbol

Parameter

Min

Max

Unit Note

ILED

Sink current @ output L

10

mA VOUT = 1V

IOUTHI

Leakage current @ output off

-10

10

µA

VOUT = 5V

VIN

Acceptable input voltage @ output off

-0.3

40

V

fBLINK

Blinking frequency

2

3

Hz

Data Communication Watchdog

AS2702 is equipped with a watchdog timer to supervise data communication by monitoring the strobe signals at pins DSTBn and

PSTBn.

If a parameter or data strobe is not followed by a consecutive strobe within a time period of 50 … 100ms, the watchdog is triggered

and initiates a ‘soft’ reset, see section Reset.

Reset

There are 2 categories of reset-events, leading to 2 slightly different reset-conditions of the slave device:

1

A ‘hard’ reset taking place at power-up and power-down of supply-voltages U5R and UOUT.

At power-up the slave device leaves reset-condition as soon as U5R has passed 3.75V and UOUT has passed VCOMOFF =

nom. 10V.

At power-down the slave device is forced into reset-condition as soon as U5R drops below 3.75V.

(Tolerance of the threshold voltages referred to is

±5 %)

2

A ‘soft’ reset, resulting from one of the following events:

2.1

Data strobe pin DSTBn is kept L for more than 100ms;

2.2

Master command ‘RESET SLAVE’ is received;

2.3

Master command ‘RESET BROADCAST’ is received;

2.4

The communication watchdog is triggered.