What is the SWD driver impedance of SWDIO line?

[godmode]

As in topic I'am concerned about the impedance of SWD interface drivers.

I'am building and SWD interface multiplexer that will be used with 48 devices using J-Link Pro debugger both for production programming and debugging.
The cables are going to be about 100 cm long (yes, I know they are long :) ).
The SWCLK and SWDIO signals will be passed by multiplexer's FETs and impedance matched by external resistor plus variable resistor.

I need to know what is the impedance of SWD drivers in nRF52832 microcontroller?

[godmode]

Thank you for all your help.
I have SWD multiplexer fully functional.
We are very happy everything is working because without JTAG support multiplexer like this is the only way to debug or flash multiple devices.
Below I have put some photos :)

It has 48 ports which multiplexes three SWD signals: VREF, SWDIO, SWCLK. GND is common.
We are using it for production: programming 40 devices takes 2 minutes at 4MHz JLink's clock,
and debugging: hardware is connected to PC and VPN, anytime we find a glitch it is possible to debug a device remotely without changing the cables.
Cables are 250cm long.
Multiplexer is controlled by scripts or standalone GUI application.

drive.google.com/folderview

[Dimitar]

Hi @godmode, looks like really nice programming setup. I probably need something like for a panel of 20x nRF51822.

Choice is between 20x standalone programmers with memory and common trigger, or something like your setup.

Using 20x nRF52 dev boards seems not a nice solution :)

Are you going to sell this as commercial product, as kit or publish the hardware/software design? In my case VREF is not needed, I think.

Thanks in advance!

[godmode]

Hi Dimitar,

I will ask at my place are they going it to sell it or not and let you know on private message.

Are you going to use JLink? If so they you need the VREF.

[Dimitar]

Currently I am using nRF52 dev.kit to program the boards, and have only 2 program plus 2 power pins.

J-link can be an option, if that will make it faster and problem free, otherwise no need for it. Of course program chips at HiLo is may be easiest, but there should be some fun, too.

[godmode]

VREF is voltage reference of target board. It is needed so the programmer/debugger can properly align the voltage signals. In your setup you need to connect pin 1 (EXT_VTG) of P19 on dev.kit to VREF. Im sure you are using P19 to programm your boards?
JLink is one of the fastest of programmers on the market and in a fact a standard at the time.
For the JLink we are suppling the automation scripts. If you are going to use the dev.kit you need to provide your own scripts or switch between the boards manually by the terminal application (cables are all connected no switching needed).

[Dimitar]

Will check the setup tomorrow and come back.

[Dimitar]

It passed a six months, and I simply missed you answered me. Do you continue using this multiplexer and script/software for it further? I try to send a PM, but I don't know if you have chance to read it.

[godmode]

I have replied to your PM :)