Dynomotion

Group: DynoMotion Message: 11222 From: Hardy Family Date: 3/15/2015
Subject: Pull-downs on aux inputs
Hi Tom,

Next time you update the kflop manual, please indicate the 150 Ohm pull-downs (and any other surprises) on the 16 aux inputs, in the hardware I/O section.  The info is buried in a section on configuring step/dir, so I missed it and my prototype breakout board doesn't work.  OK, this time I blasted off the 150 ohm resistor packs, and it works now, but somebody else might run into this issue.

Why do you have such heavy pull-downs?  Line termination?  I use most of those pins for inputs, and the sources are fairly high impedance because of the noise filtering, 5->3V conversion, and ESD protection, so I now need to insert a buffer.  Since it takes 20mA to drive each one high, it's a bit hard to find an octal driver that can push 160mA continuously.  For example, the SN74LVC541A has 24mA drivers, but limited to 50mA for the whole package.  So I'm still looking...

Regards,
SJH
Group: DynoMotion Message: 11225 From: Tom Kerekes Date: 3/16/2015
Subject: Re: Pull-downs on aux inputs
Hi SJH,

Yes the heavy 150ohm pull downs are for termination.  Otherwise it seems hard to get high data rates through ribbon cable.

I thought we documented the termination pretty clearly here:
 

JP4 - Aux Connector #0
Auxiliary connector which supplies power, reset, and 10 digital I/O (LVTTL 3.3V only) which is normally connected to optional expansion daughter boards (ie. SnapAmp 1000).  If no expansion module is required, these digital I/O may be used for general purpose use.  The first 8 IO (IO16-IO23) contain 150ohm termination resistors (pull downs).

JP6 - Aux Connector #1
Auxiliary connector which supplies power, reset, and 10 digital I/O (LVTTL 3.3V only) which is normally connected to optional expansion daughter boards (ie. SnapAmp 1000).  If no expansion module is required, these digital I/O may be used for general purpose use.  The first 8 IO (IO26-IO33) contain 150ohm termination resistors (pull downs).

Regards
TK


Group: DynoMotion Message: 11226 From: Hardy Family Date: 3/16/2015
Subject: Re: Pull-downs on aux inputs
OK, I see it now, it's on the web page version.  Trouble is, I was using the big PDF (dated 2011) with everything combined - it doesn't seem to have that text.

Regards,
SJH



On Mon, Mar 16, 2015 at 9:33 AM, Tom Kerekes tk@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:
 

Hi SJH,

Yes the heavy 150ohm pull downs are for termination.  Otherwise it seems hard to get high data rates through ribbon cable.

I thought we documented the termination pretty clearly here:
 

JP4 - Aux Connector #0
Auxiliary connector which supplies power, reset, and 10 digital I/O (LVTTL 3.3V only) which is normally connected to optional expansion daughter boards (ie. SnapAmp 1000).  If no expansion module is required, these digital I/O may be used for general purpose use.  The first 8 IO (IO16-IO23) contain 150ohm termination resistors (pull downs).

JP6 - Aux Connector #1
Auxiliary connector which supplies power, reset, and 10 digital I/O (LVTTL 3.3V only) which is normally connected to optional expansion daughter boards (ie. SnapAmp 1000).  If no expansion module is required, these digital I/O may be used for general purpose use.  The first 8 IO (IO26-IO33) contain 150ohm termination resistors (pull downs).

Regards
TK