Control Techniques Digitax ST Advanced User's Manual page 66

Parameter
Menu 3
structure
The following is an example of the response when the Encoder to send position command is used (encoder to drive).
LS byte
MS byte
The example shown above is for an encoder with 12 bits representing the turns and 13 bits representing the position within a turn. The position
command only requires one byte to be sent to the encoder. Bits 14 and 13 can both be set in the transmit register if required to indicate that this is
both the first and last byte of the message.
If any other command is used then the response is as follows (encoder to drive).
Address
Data (LSB)
Data (MSB)
Example of EnDat transfer: Read position
Disable drive encoder position check by setting Pr 90.21 to one. This should be set back to zero at the end of the transfer if encoder position checking
is required.
Transfer the "read position" message to the encoder comms buffer by writing the sequence of words shown in the table below to Pr 90.22. A check
should be carried out before each word is written to ensure that the parameter is zero (i.e. the drive has taken any previous data).
Bit 15 Bit 14
0xa000 1
0xc000 1
The second word contains the address which is not required for the command, but has been passed to the drive so that a word with bit 14 set to one
is received by the drive to initiate the data transfer to the encoder. When the encoder response has been received by the drive the first byte of the
message will be placed in the least significant byte of Pr 90.23 and bit 15 will be set to one. This data should be read and the parameter cleared so
that the drive will put the next byte into this parameter. The sequence of data that could appear in Pr 90.23 for an encoder with 12 turns bits and 13
position bits is shown in the table below.
Bit 15 Bit 14
0x8000 1
0x8000 1
0x8000 1
0x8000 1
0x8000 1
0x809f 1
0x804e 1
0xc074 1
Turns = 0111 0100 0100 = 0x744
Position = 1 1101 0011 1110 = 0x1d3e
Alarm bit = 0
Example of EnDat transfer: Encoder send parameter
Data written to Pr 90.22
Bit 15 Bit 14
0xa004 1
0x8000 1
0x8000 1
0xc000 1
66
Keypad and
Parameter x.00
display
st
1 byte
th
8 byte
st
1 byte
rd
3 byte
Bit 13 Data
0 1 0x00 Read position command
1 0 0x00 Address
Bit 13 Data
0 0 0x00
0 0 0x00
0 0 0x00
0 0 0x00
0 0 0x00 Bit7 = bit 0 of position, Bit6 = alarm bit
0 0 0x9f Bits 8-1 of position
0 0 0x4e Bits 3-0 of turns and 12-9 of position
1 0 0x74 Bits 11-4 of turns
Bit 13 Data
0 1 0x04 Encoder to send parameter command
0 0 0x00 Address zero
0 0 0x00 Data (not required)
1 0 0x00 Data (not required)
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Parameter Advanced parameter
description format descriptions
Bits 7-0 = 0
Bits 7-0 = 0
Bits 7-0 = 0
Bits 7-0 = 0
Bits 5-0 = 0
Bits 6 = Alarm bit
Bits 7 = Bit 0 of position
Bits 7-0 = Bits 8-1 of position
Bits 3-0 = Bits 12-9 of position
Bits 7-4 = Bits 3-0 of turns
Bits 7-0 = Bits 11-4 of turns
Serial comms Electronic
Performance
protocol nameplate
Digitax ST Advanced User Guide
Issue Number: 1