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TH3044.2A

K-Bus Interface

Melexis Microelectronic Systems  

TH3044

K-Bus Interface

Bit Compare

Are the signals at the pin TxD and the pin BUS

within a specified time t bc not identical, the

transmission will be interrupted.

If both signals at TxD and BUS are “High”

within the time t ena the transmission will be

enabled. To switch the TH3044 into the

receive mode a low level “0” has to be applied

to the pin Bus. If the TH3044 is part of a

complex bus system the first device which

transmits a low level “0” to the bus line forces

all other TH3044 to switch into the receive

mode. This state is valid until tena .

The bitcompare-function is frequently retrig-

gered by every new bit-comparison of two

different levels.

The bit-compare-function is activ when the pin

SEN/STA is open (not overwritten).

Constant Low

A falling edge at pin TxD (from “1” to “0”) starts

the internal constant low timer.

If the low level “0” is valid for the time t low the

transmission unit of the TH3044 will be

disabled.

The receive unit is still active. A high level “1”

at TxD with a minimum pulse width of t resets

the constant low timer.

t < trec

TxD

SEN/STA

TxD

tlow

tena

BUS

SEN/STA

t < tbc

tena

tb c

tena

Undervoltage

Undervoltage at pin VBAT or pin VCC doesn’t

occur an unwanted low level at pin Bus (see

chapter “Transmit”)

SEN/STA

The pin SEN/STA is bidirectional. Used as an

output the pin indicates whether the transmit-

path is enabled or disabled:

SEN/STA =”0”

transmission path is enabled

SEN/STA =”1”

transmission path is disabled

Using this pin as an input the transmission

path can be overwritten (independent of bit-

compare and constant-low function):

SEN/STA=”0”

forcing the transmission path free

SEN/STA=”1”

disable the transmission path

3901003044

Rev. 003

Page 6

Nov/02

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