HM 10 Pinout

No	Name	Description	CC2541 Pin Name (Description)
1	UART_TX	UART Interface	P1_6
2	UART_RX	UART Interface	P1_7
3	UART_CTS	UART Interface	P1_4
4	UART_RTS	UART Interface	P1_5
5	NC	No connection
6	NC	No connection
7	NC	No connection	P2_2 (Debug clock)
8	NC	No connection	P2_1 (Debug data)
9	NC	No connection	P2_0
10	NC	No connection
11	RESETB	Reset if low longer than 100ms	RESET_N
12	VCC	3.3v
13	GND	Ground
14	GND	Ground
15	SCL	I2C Interface	2
16	NC	No connection
17	NC	No connection
18	NC	No connection
19	NC	No connection
20	SDA	I2C Interface	3
21	GND	Ground
22	GND	Ground
23	PIO0	System key	P1_3
24	PIO1	System LED	P1_2
25	PIO2	Programmable input/output line	P1_1
26	PIO3	Programmable input/output line	P1_0
27	PIO4	Programmable input/output line	P0_7
28	PIO5	Programmable input/output line	P0_6
29	PIO6	Programmable input/output line	P0_5
30	PIO7	Programmable input/output line	P0_4
31	PIO8	Programmable input/output line	P0_3
32	PIO9	Programmable input/output line	P0_2
33	PI10	Programmable input/output line	P0_1
34	PI11	Programmable input/output line	P0_0

Pulled from the HM-10 datasheet and referenced with the CC2541 datasheet. Note that sometime in the middle of 2014, HM-10s started shipping with CC2541s instead of CC2540s. The differences are minor.

To use with the CC Debugger, connect P2_1 (debug data), P2_2 (debug clock), RESETB, GND and VCC (only if you want the debugger to power the board). See the CC Debugger pinout here.

Other sources claim that some of the unconnected pins are PCM audio pins. This is false.