Xtend GPIO characteristics

Does anyone know the electrical characteristics for GPIO21/25 on the Xtend power cable ? These are referenced to Vref (I’m using 5.0V) and appear to have pretty strong internal pull-ups (I’m using them as inputs connected to open-collector opto-couplers). I’ve managed to get something working but its been trial and error and not satisfactory.

There are details in the current User Guide…

To finish this story - I’ve set Vref to 5.0V and pulled each GPIO down to Gnd using 1K8 resistors. PS2811 opto-couplers pull up the GPIO when required. One of the GPIO (21) seems to be set as an output (pulled strongly high) for quite a few seconds while the modem starts up, but there’s nothing I can do about that.

I have a similar problem on the GPIO, according to the user guide it is suggested to tie the Vref for the IO voltage to a fixed voltage ie 5.0v. however if i measure the high value of the GPIO it goes only as high as 1.8V in a output mode it never reaches the 5.0v level. is there any specific trick to get it to the level of the vref?


Please ignore the post, the GPIO pin doe go to the Vref if no load is available however the pin is pulled high through a 100k resistor to vref which makes the current flow verry little and not enough to drive what i needed it to drive.