I'm designing a Printed Circuit Board (PCB) for and embedded system currently in development. I am using a BL652 DVK from Laird and using SWD programming with Keil uVision 5 and Nordic SDK v15.0.0 to write software and debug. I plan on replacing the DVK with this custom PCB, using SWDIO, SWDCLK and SWO for debugging and the former two for programming the BL652 on board. Page 11 of the datasheet of the Development Kit I'm using (found here: https://assets.lairdtech.com/home/brandworld/files/BL652%20Dev%20Kit%20User%20Guide.pdf) clearly shows how the programmer is connected to the BL652. However, when searching through ARMs documentation of the proper connections for SWD programming (referring to this web page here: https://developer.arm.com/docs/100956/latest/arm-dstream-target-interface-connections/signal-descriptions/serial-wire-debug#pge1418217065224), they bring up two issues:
1.) Pull up resistors must be connected to the serial wire lines to hold them stable when the programmer is disconnected.
2.) The sum of the impedance of the "driver" (I'm assuming that's the external programmer) and an additional series resistor must be matched to 50 Ohms.
After searching elsewhere on the internet, I haven't found much about these two subjects. After reading one Question and answer here on Nordic DevZone (What is the SWD driver impedance of SWDIO line?), I began to doubt the importance of taking action on the two concerns ARM brought up. I did find some information on the setup of the nRF52832 internals, on page 70 of its datasheet, saying that the SWDIO line has an internall pull up and the SWDCLK line has an internal pull down resistor. To me, it makes no sense to have a pull up AND pull down resistor on the same line, as ARM is implying. I would assume that p0.18 (the GPIO usually assigned to the SWO line) has no such internal resistor circuit.
How should I proceed? Do I need to worry about the topics brought up by the ARM webpage?
