Production SWD/SCLK Multiplexing?

[Shay Ohayon]

We need a fast way to do production testing on our boards (based on nrf52832). They have multiple peripherals that we would like to make sure were soldered correctly.

I was thinking about a way to route all SWD and SCLK signals from multiple boards on the single panel to a connector.

To reduce costs of having to connect multiple programmers, I was wondering if it is possible to route all those SCLK and SWD with a multiplexer - to a single programmer - and then program each of the boards serially.

What would be the requirements for such a multiplexer?

[slowcoder]

If you only considering production testing, here's how it's usually done in high-volume production.

It's not common to test the whole panel with one connector. It sounds like a good idea, but routing traces out from the individual PCBs into the panel is usually a yield-loss drivers, as the traces might (and do) get shorted when you cut or route them out from the panel.

So, if we concentrate on testing a single PCB, there's usually at least four test-points that a "bed of nails" test-jig can attach to. VCC,GND,UART_TX and "TESTMODE".

When the device starts up, it checks the testmode pin, and if it's shorted to ground, the device enters a self-test mode, and outputs the results over UART.

Why is it done this way? Well, UART is the least common denominator when it comes to various embedded devices (anything from 8bit micros to 64bit SOCs support it). Also, a USB<>UART converter is super-cheap, so the factory can buy as many as they need.