Overflow biss-c 32 bit encoder

[RafaelFalcaro]

Hi, I have a stepper configured on PowerPMAC BrickLV Firmware 2.5.4.0, using a biss-c 32-bit encoder as position feedback, configured as follow:

 

Encoder:

Acc84B[0].Chan[2].SerialEncCmd = $2114A0

EncTable[13].type = 2
EncTable[13].pEnc = Acc84B[0].Chan[2].SerialEncDataA.a
EncTable[13].pEnc1 = Acc84B[0].Chan[2].SerialEncDataB.a
EncTable[13].index1 = 0
EncTable[13].index2 = 0
EncTable[13].index3 = 0
EncTable[13].index4 = 0
EncTable[13].index5 = 0
EncTable[13].index6 = 0
EncTable[13].ScaleFactor = -1

 

Motor (snippet):

Motor[3].pEnc = EncTable[13].a
Motor[3].pEnc2 = EncTable[3].a

Motor[3].PowerOnMode = 4
Motor[3].AbsPosFormat = $00082008
Motor[3].pAbsPos = Acc84B[0].Chan[2].SerialEncDataA.a
Motor[3].pAbsPos2 = Acc84B[0].Chan[2].SerialEncDataB.a
Motor[3].AbsPosSF = -1

 

I'm facing a problem with power on position settings, due to overflow on Acc84B[0].Chan[2].SerialEncDataA register. There are two experiments of executing #3hmz command on terminal on two different positions of my stage course (see WatchWindow with SerialEncData registers):

 

 

 

From position 1 to position 2, I executed a #3j+ command on terminal, and after some seconds, I executed #3j/ and #3hmz commands. The expected behaviour on position 2 is a positive value, not the overflow seen in the test.

 

 

Is there a power on position setting which fix this problem?

 

[RafaelFalcaro]

Hi, I fixed the problem by changing:

 

Motor[3].AbsPosFormat = $01082008

 

[MoMo]

I think your encoder conversion table does not need to use type=2.

Generally speaking, when it is used as an incremental position, you only need to obtain the low-bit data.

The absolute value position only needs to be obtained when the system is started.

[steve.milici]

What MoMo says is very true. A type 2 ECT entry to read the second register is not necessary unless it is possible for the source data to change by half the range or more of the “SerialEncDataA” 24-bit register in a single servo cycle. In this case a type = 1 single register read is recommended, as it saves both hardware access time, and software computation time.