# Test point map for BBC micro:bit

Does anyone have a map of the test points on the BBC micro:bit?

Specifically, I'd like to connect a scope to the lines from the nRF51's UART to the USB chip, which the published schematic suggests are connected to two test points. Among other things, that will enable us to measure the inter-character delay caused by interrupt handling vs polling and simultanously see the output on a host computer.

I'm not reluctant to probe around myself, but I'd rather save some time ...

• The NRF51 on the micro:bit can map its UART functios to any GPIO pin. Not sure why you would need to probe stuff here. – Turbo J May 11 '18 at 18:42
• The default baud rate doesn't match the docs, from what I remember... – Sean Houlihane May 11 '18 at 19:59
• @SeanHoulihane I seem to remember the same (9600 vs 115200 baud?), but I'm not using any of the supplied firmware, so that's not bothering me. If I pin down the source of the inconsistency, I will be sure to post it somewhere. – Mike Spivey May 11 '18 at 23:43
• @MikeSpivey Updated my answer. Concur on 9600 Baud. – Sean Houlihane May 12 '18 at 15:10

The testpoint map is available in this PR, which seems to be stalled on getting merged (which would explain why you haven't found it).

This image is Copyright BBC, CC-CY-4.0

The signal names are as follows, according to the schematic.

 1 TMS  -- Debug interface for KL26
2 TDO  --  "
3 TDI  --  "
4 TCLK --  "
5 RST* --  "
6 TGT_SWDIO
7 TGT_SWCLK
8 KL26 XTAL -- has 16MHz sine wave
9 GND
10 VBUS_IF -- carries 5V when USB plugged in
11 USB-D+
12 USB-D-
13 VBAT
14 +V_TGT
15 TGT_TX -- UART transmit from nRF51
16 +3.3V_IF
17 TGT_RX -- UART receive from nRF51
18 VBAT
19 GND
20 TGT_RESET
21 GND
22 GND


In particular, the two UART lines are accessible at TP15 and TP17.