getting sometimes wrong values from Ultrasonic Sensor then i read more than 1 Byte at a time.

[Grobi71]

Hello,

i want to read more than 1 Byte with one read cycle. I tried it with the Ultasonic Sensor and get nearly

every 2nd read wrong Values. I try to read from Register 8  5 bytes. This is the result

byte  1. read   2.read   3.read  4. read 

1)      76              69        76        76

2)      69              71        0          69

3)      71              79        71        71

4)      79              0          79        79

5)      0                0           0          0

and so on. Right is 76 69 71 79 0  which means LEGO

does anyone have an Idea ?  I put the vi into the Attachment

[Grobi71]

Hello all,

i found my mistake. If you read out the Senor, the bytes read have to be the same count of bytes as discribed in the Documentation.

So if you want to read Register 8 you have to read 8 bytes. If you want to read register 42h you have to read 1 byte.

If you do not so you will get strange Values back.

rgds

Harald

[pnitin]

I Guess you are haveing problems of buffer wraping,
NXT has I2C buffer of 16 bytes and wnen you cross this boundry you have problems
that may be the reason you do not see  it when you read 8 bytes ( it should work for 4 as well)

[Grobi71]

Hi,

i tested it with an EEProm and it works everytime with the Buffersize i choosed. With the US-Sensor it does not.

i think the Problem is the Programming of the MCU inside the US-Sensor. It wants to deliver a count of Bytes. If it

is not able to do it, it will be instable for an amount of reads. If i choose the amount of Bytes the US-Sensor wants to deliver

it is stable every read.

rgds

Harald