The board has push button on PTA4 and LED on PTD7. The button works as 'a' key and the LED as an indicator for capslock.
+ELF board
+---------
+This board acommodates 48QFN chip.
+
+### prototypte pinout
+- pcb layout https://deskthority.net/resources/image/33293
+- schematic https://deskthority.net/resources/image/33252
+
+
+ 39 ..... 44 \ conn / 1 ..... 6
+ 38 |______| LED 7
+ : Rst :
+ : :
+ 32 Bl 13
+ 31 .........24 23............ 14
+
+ 1 PTD6 12 PTC3 23 GND 34 PTE20*
+ 2 PTD5 13 PTC2 24 PTA18 35 PTA20 Reset
+ 3 PTD4 14 PTC1 25 3.3V 36 PTA3 SWD_DIO
+ 4 PTD3* 15 PTC0* 26 PTA4 NMI 37 PTA0 SWD_CLK
+ 5 PTD2* 16 PTB17* 27 PTA2 38 3.3V
+ 6 PTD1* 17 PTB16* 28 PTA1 39 GND
+ 7 PTD0* 18 PTB3* 29 PTE25* 40 VBUS VREGIN
+ 8 PTC7 19 PTB2* 30 PTE24* 41 USB D-
+ 9 PTC6 20 PTB1 31 PTE30 42 USB D+
+ 10 PTC5 21 PTB0 32 PTE29* 43 GND
+ 11 PTC4 22 PTA19 33 PTE21* 44 USB Shield
+
+
+TMK KL27Z breakout
+------------------
+This board acommodates 48QFN chip.
+
+### Pinputs
+
+ _\ conn /_
+ 1 28
+ : :
+ : PROG :
+ : RST :
+ 14 15
+ ----------
+
+ 1 VUSB 28 GND
+ 2 VIN VREGIN 27 PTD4
+ 3 PTD5 26 PTC7
+ 4 PTD6 25 PTC6
+ 5 PTD7 24 PTC5
+ 6 PTE0* 23 PTC4
+
+ 7 3.3V 22 GND
+ 8 PTE30 21 PTC3
+ 9 PTA0 SWD_CLK 20 PTC2
+ 10 PTA1 19 PTC1
+ 11 PTA2 18 PTB1
+ 12 PTA3 SWD_DIO 17 PTB0
+ 13 PTA4 NMI 16 PTA20 Reset
+ 14 PTA18 15 PTA19
+
+
+#### Pinouts difference between 32QFN and 48QFN
+48QFN doesn't have PTE0
+32QFN doesn't have PTD0-3, PTC0, PTE20-21,24,25,29, PTB2-3,16,17
+
+### ROM bootloader pins
+See Reference Manual Chapter 13.
+
+ PTA2 LPUART0_TX
+ PTA1 LPUART0_RX *
+ PTB0 I2C0_SCL
+ PTB1 I2C0_SDA
+ PTC4 SPI0_SS_b *
+ PTC7 SPI0_MISO
+ PTC6 SPI0_MOSI
+ PTC5 SPI0_SCK *
+
+Due to errata e9457, need to pull-up `SPI0_SS_b`(or `SPI0_SCK`) to prevent false detection of SPI.
+The errata doesn't refer UART though, `LPUART0_RX` also requires pull-up or down resisitor from experience.
+Without resistor it easily false-detects activity on UART interface with finger touch on the pin.
+
+
+
+
Resources
---------
+### Deskthority thread
+https://deskthority.net/workshop-f7/can-we-design-the-teensy-alternative-for-keyboards-t13662-510.html
+
### Kinetis KL2x
http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/kinetis-cortex-m-mcus/l-series-ultra-low-power-m0-plus/kinetis-kl2x-48-mhz-usb-ultra-low-power-microcontrollers-based-on-arm-cortex-m0-plus:KL2x