8
DATA OUTPUT FORMAT
Data is output serially with the first bit being status (STA). The status bit is high when
virtual absolute position is not known. After a small initial movement the status bit
should go low and stay low. The second bit is the MSB of the position word. Following
the LSB of the position word are three flags bits. Flag 1 goes high when a decoding error
occurs. Flag 2 goes high when either the analog signal amplitudes become too low ( Sin
or Cosine < 1Vpp) or the Index signal transitions are occurring in the wrong place. Flag
3 goes high when a quadrature error is detected. This occurs if SIN and COS states
change by more than 90 degrees between a sample. A flag bit is set by an error and will
be held until a read is completed. The next bit is a parity bit. The parity of all the bits is
odd.
TABLE 2: Data format
BIT POSITION
BIT NAME
DESCRIPTION
Bit 1
STA
VA Decoder Status Bit.
Bit 2 thru Bit (n+1)
D
MSB
..
D
LSB
Position bits.
Bit (n+2)
Flag 3
Quadrature error.
Bit (n+3)
Flag 2
Signal quality watchdog.
Bit (n+4)
Flag 1
VA decoder error.
Bit (n+5)
Parity
Parity bit. Parity is odd.
Bit (n+6)
(0 bit)
Trailing zero bit.
* n is the number of position bits
Содержание VJ
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