Data representation by PLC on PROFIBUS-DP network

[arbj]

Hi,

I have a small question regarding representation of 16 bit data by PLC.

I have a parameter that uses 16 bit data. I have thought of using two ways of representing this data on the PLC data registers.

I would like to know which of these two methods is commonly used in usual practice ?? Or is there any other commonly used method ??

1. Using HEX format.

Say if the data is 1600 (Decimal), then in HEX format this would be represented in two bytes as

Byte 1= 06 (MSB)
Byte 2= 40 (LSB)

2. Using packed BCD format

Data in decimal format is 1600

Byte 1= 16 (MSB)
Byte 2= 00 (LSB)

Data in decimal format is 300

Byte 1= 03 (MSB)
Byte 2= 00 (LSB)

thanks
a

 

[KalleOlsen]

Do not use BCD, it is NOT common.

That format is an anachronism from the ancient times when the thumb wheel selectors ruled ;P

Kalle

 

[arbj]

Thanks kalle, I won't be using BCD...

So is the hex format the commnlt used method ??

Also how can negative values be represented ???

thanks
a

 

[KalleOlsen]

Also how can negative values be represented ???

thanks
a

This is a very basic question.


As a 16 bit signed integer.

HEX SINT
0000 0
0001 1
FFFF -1
7FFF 32767
8000 -32768

And finally a link:
http://www.plcdev.com/step_7_elementary_data_types


Kalle

 

[JesperMP]

The almost universally used coding of integers used in PLCs and computers is called "two's complement". It is the same that Kalle describes.