Wednesday, 24 February 2021

How to add 7i85 board to 5i25/7i76 combo

Although I'm not quite ready to integrate my X and Z linear encoders with my LinuxCNC system, I have the 7i85 board already. I 'll need that to support the extra encoders above the single instance that the 7i76 supports. generally that's going to be used for the spindle encoder that you'll want if you want to measure actual spindle speed and the all-important rigid tapping.

Here's an overview of some of the Mesa cards.

The 7i85 is a "dumb" card ie it has no FPGA onboard, so doesn't require reflashing to set up the various IO. Instead, the 5i25 within the PC needs to be told to expect a 7i85 to appear on the end of the 25 way parallel cable.

The default firmware provided in the 5i25 when they ship it is configured for 1 or 2 of the 7i76 daughterboards. So I need to change the firmware within the 5i25. There's a bitfile for a 7i76 / 7i85 pairing, so the process is like this:

  • Download the 5i25 zip file from Mesa Electronics containing all the available bitfiles.
  • Use the mesaflash utility to flash the 5i25_7i76_7i85.bit bitfile into the 5i25.
  • Reboot the PC to power cycle the 5i25 so the changes take effect (yes I forgot).
The 7i76 should continue to operate as before (no need to reconfigure it). The 7i85 (being a dumb board) should simply appear as additional IO on the 5i25 board. In this case I should be able to set up as many as 4(?) encoder inputs and something like 5 RS485 interfaces.

Luckily, mesaflash is included in the std LinuxCNC install, so as long as you avoid capitalising the first letter and remember to issue the sudo command first, it will go like this:

muzzer@LinuxCNC:/lib/firmware/hm2/5i25/configs/hostmot2$ sudo mesaflash --device 5i25 --write 5i25_7i76_7i85.bit
Checking file... OK
File type: BIT file
Boot sector OK
EEPROM sectors to write: 6, max sectors in area: 16
Erasing EEPROM sectors starting from 0x100000...
Programming EEPROM sectors starting from 0x100000...
Board configuration updated successfully.
Checking file... OK
File type: BIT file
Boot sector OK
Verifying EEPROM sectors starting from 0x100000...
Board configuration verified successfully.

You must power cycle the hardware or use the --reload command to load a new firmware.

That worked and the 7i76 config remained intact - TFFT!

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