Mesa 7i77 support for absolute linear encoder

PCW wrote:

I can make a 7I77 config for a 5I25/6I25 with one SSI or BISS
interface on the serial expansion, but it may take a couple days
as I am pretty busy currently.
 

I understand.. But help me choose: On the surface it looks like BISS is faster and made to be better than SSI. Renishaw encoders mentions it to be BISS-C. The sales representative was cool enough to give me access to all there encoders to connect and choose the suitable one. 6i25,7i76 and 7i77 are all I have. Should I go with BISS-C or stick with SSI protocol encoder if I have to choose without testing both variants?
Or is it better to make necessary firmwares to test the variants and then make the choice?

I'll order 7i74 for final use.

Can I ask a question. On what machine will you put these linear encoders? Do you really need absolute position?
If it is not a secret, what is the price of these encoders?
When I bought my ethercat servo motors I thought this was the only way to always have an exact position

besriworld wrote:

Can I ask a question. On what machine will you put these linear encoders? Do you really need absolute position?
If it is not a secret, what is the price of these encoders?
When I bought my ethercat servo motors I thought this was the only way to always have an exact position

Its for a 4 axis machine I've designed for milling and tapping a very small component continuously about 2500 components per day. This is a new development project to check the viability of inhouse machine for production. 2 meters long rectangular bar is fed through the 4th axis to machine, and we thought of using linear encoder instead of motor shaft mounted encoders based off our previous experience. Absolute and incremental encoders has approximately 30 percent price difference and our approach is to minimize the number of components like homing switches to streamline our design more than absolute position although absolute encoder is going to be useful during power cuts which we have a few times in a month. 
Renishaw quoted price for two variants: 4400 INR for 440mm absolute scale AS10(40micron accuracy) and 23200 INR for 488mm absolute scale SAS10(20micron accuracy) with reader head which can be used on either scale that we choose LA11 at 24000 INR

I've used very expensive fuji AC smart servo 5 drives and motors with absolute position in the past: Measuring the position as close to the desired work piece eliminates unnecessary precision components in the chain like motor shaft couplings, ball screw and guideways in my experience.

Yes that is right !
The linear encoder gives precision. I also bought linear encoders but they are not absolute position.
The price sounds good.

5I25/6I25 configuration for 7I77 with one BISS interface
on the 7I77s serial expansion port:

 

5I25/6I25 configuration for 7I77 with one BISS interfaceon the 7I77s serial expansion port:

 

File Attachment:

File Name: 5i25_7i77x2_bissd.zip
File Size:95 KB

Thanks a lot. I have flashed the firmware and the pins 3,4 show data in and pins 5,6 show clock out on TB6. Now in the main HAL file made using pncconf, chooisng 5i25 board with 7i77x2 with one 7i77 firmware, I have loadrt hm2_pci config="num_encoders=6 num_pwmgens=0 num_stepgens=0 sserial_port_0=003xxxxx" 
Now I read about:

SOFTWARE PROCESS DATA MODESThe 7I77's digital I/O section (normally on sserial channel 0) has 4 software selectable process data modes. These different modes select different sets of 7I77 data to be transferred between the host and the 7I77 during real time process data exchanges. For high speed applications, choosing the correct mode can reduce the data transfer sizes, resulting in higher maximum update rates.MODE 0 I/O only mode (32 bits of input data, 16 bit of output data)


MODE 1 I/O plus analog input mode (32 bits of input data, 16 bits of output data, 4 analog input channels on inputs 0..3)
MODE 2 I/O plus analog input and field voltage mode (32 bits of input data, 16 bits of output data, 4 analog input channels (on inputs 0..3) and field voltage analog in)
MODE 3 I/O plus analog input and field voltage mode (32 bits of input data, 16 bits of output data, 4 analog input channels (on inputs 0..3), field voltage analog in and 2 MPG encoders on inputs 16..19). Default encoder count mode is 1X to match normal 100 PPR MPGs. Encoder input threshold is fixed at 2.5V for compatibility with 5V encoder outputs.

I am not sure how configure the HAL file to map the RS422 pins to joint 0 encoder inputs. I am trying copying from a lot of online available lines from HAL configurations but I have been unable to make it work. I need a little help figuring this out. 
I have HOME_ABSOLUTE_ENCODER = 1 set in the axis ini file.
 

tommylight wrote:

See my previous link, it has hal files for serial absolute encoders, those do require a few more lines in hal to work.

Those are fairly standard firmware with standard functions buddy. PCW had written a firmware to make the serial RS422 port to take BISS protocol encoder I/O. I don't know if syntax like "net x-pos-fb <= hm2_5i25.0.biss.01.xencoder.position" would work as I don't know if it is labelled as encoder 01.
I am asking before hand just because the encoders are just lent to us for checking when we are sure of it working to a high probability. I have been reading through the documents there is a lot to cover.

You should read the hostmot2 manual page, BISS section

man hostmot2

Then search for BISS

The main things needed in the hal file are the proper format string for your particular encoder and setting up the DPLL to trigger reads before the nominal LinuxCNC read time

PCW wrote:

You should read the hostmot2 manual page, BISS section

man hostmot2

Then search for BISS

The main things needed in the hal file are the proper format string for your particular encoder and setting up the DPLL to trigger reads before the nominal LinuxCNC read time

Should there be the modparam: sserial_port_0=NNNNNNNN in loadrt hm2_pci config in the HAL file because, I'm guessing the firmware you wrote is meant to replace sserial port on 7i77 with a BISS encoder port. 
The sserial shows under the hm2>7i77>0 in the HAL configuration and I don't know if that should be the case.
The hm2_<BoardType>.<BoardNum>.dpll.NN.timer-us always through an error: pin not found while starting linuxcnc.
Without the dpll line, linuxcnc starts but shows couldn't read data: you should set dpll timer. I couldn't get it fixed.
I don't know what I'm missing, I have read through the man page for hostmot2 multiple times, couldn't make the encoder spit out any data nor could I get any clock pulses through tx+ tx- pins 5,6 (TB6) when connected to external oscilloscope (Renishaw technical person told the encoder needs to get the clock pulses only then it will spit the position data)
Has anyone done BISS encoder on 7i77 before?