User's Manual

Geo MACRO Drive User and Reference Manual

Geo Macro Drive MI-Variable Reference 145

When MI914 is set to 1, the encoder index channel input (CHCn) is logically combined with (“gated by”)

the quadrature signals of Encoder n before going to the position capture circuitry. The intent is to get a

“gated index” signal exactly one quadrature state wide. This provides a more accurate and repeatable

capture, and makes the use of the capture function to confirm the proper number of counts per revolution

very straightforward.

In order for the gated index capture to work reliably, the index pulse must reliably span one, but only one,

“high-high” or “low-low” AB quadrature state of the encoder. MI915 allows you to select which of these

two possibilities is used.

MS{node},MI915 Primary Encoder Index Gate State/Demux Control

Range: 0 - 3

Units: 0 = Gate index with “high-high” quadrature state (GI = A & B & C)

1 = Gate index with “low-low” quadrature state (GI = A/ & B/ & C)

2 or 3 = De-multiplex hall and index from third channel, gating irrelevant

Default: 0

MI915 is a 2-bit variable that controls two functions for the index channel of the encoder.

When using the gated index feature of a PMAC2-style Servo IC for more accurate position capture

(MI914=1), bit 0 of MI915 specifies whether the raw index-channel signal fed into the Encoder is passed

through to the position capture signal only on the high-high quadrature state (bit 0 = 0), or only on the

low-low quadrature state (bit 0 = 1).

Bit 1 of MI915 controls whether the Servo IC de-multiplexes the index pulse and the three hall-style

commutation states from the third channel based on the quadrature state, as with Yaskawa incremental

encoders. If bit 1 is set to 0, this de-multiplexing function is not performed, and the signal on the C

channel of the encoder is used as the index only. If bit 1 is set to 1, the Servo IC breaks out the third-

channel signal into four separate values, one for each of the four possible AB-quadrature states. The de-

multiplexed hall commutation states can be used to provide power-on phase position using Ixx81 and

Ixx91.

The following table shows what hall or index state is broken out for each of the four quadrature states:

A B C

1 1 Z

1 0 U

0 0 V

0 1 W