ARM Embedded Tutorial - Simple GPIO on and off output: what changed

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Title: ARM Embedded Tutorial - Simple GPIO on and off output

New		Line
1	+	# Easy GPIO input and output
2	+
3	+	A port consists of 16 pins, which is why the lower 16 bits are used in most registers.
4	+
5	+	Exception: CRx and BSRR, with BSRR you can use the upper 16 bits to set pins.
6	+
7	+	## Port access registers
8	+
9	+	The following registers are available for GPIO access:
10	+
11	+	- CRL - Configuration Register Low
12	+	- CRH - Configuration Register High
13	+	- IDR - Input Data Register
14	+	- ODR - Output Data Register
15	+	- BSRR - Bit Set Reset Register
16	+	- BRR - Bit Reset Register
17	+	- LCKR - Port Configuration Lock Register
18	+
19	+	With all registers except CRL and CRH, each bit corresponds to a microcontroller pin.
20	+
21	+	## Switch on GPIO
22	+
23	+	Before you can access the GPIO, you have to switch it on. Without doing this, no access is possible! This is done as follows for the PortA - PortC.
24	+
25	+	``` pascal
26	+	RCC.APB2ENR := RCC.APB2ENR or (% 111 shl 2);
27	+	```
28	+
29	+	## Direct port manipulation
30	+
31	+	Before you can switch a GPIO pin to HIGH, you have to configure it as an output. This is done via the CRL and CRH registers.
32	+
33	+	I usually choose Pin 13 of Port C for these mini-examples, because the LED of the STM32F103C is connected to this pin.
34	+
35	+	Attention: The LED lights up as the anode is connected to the power supply.
36	+
37	+	### CRx - Set pin function
38	+
39	+	One nibble (4 bit) is available for the function setting. Pin 13 of Port C on output. Since 13 is higher than 7, the HIGH register CRH is used for this. 13 - 8 = 5; It is the fifth nibble in CHR. Pin0 - Pin7 would be configured with CHL.
40	+
41	+	``` pascal
42	+	PortC.CRH := $00300000;
43	+	```
44	+
45	+	### IDR - Read out entire port
46	+
47	+	``` pascal
48	+	// Is Pin 13 HIGH?
49	+	Result := PortC.ODR and (1 shl 13) > 0;
50	+	```
51	+
52	+	### ODR - Write entire port
53	+
54	+	With this function, the whole port is written at once.
55	+
56	+	``` pascal
57	+	// Only pin13 is set to HIGH.
58	+	PortC.ODR := 1 shl 13;
59	+
60	+	// All pin on LOW.
61	+	PortC.ODR := 0;
62	+	```
63	+
64	+	### BSRR - Single pin to LOW
65	+
66	+	With this function, you can set individual pins to LOW.
67	+
68	+	``` pascal
69	+	// Only set pin13 to LOW, the others remain unchanged.
70	+	PortC.BSRR := 1 shl 13;
71	+	```
72	+
73	+	### BSRR - Change the entire port using the bit mask
74	+
75	+	With this function, you can set individual pins to LOW.
76	+
77	+	``` pascal
78	+	// Only set Pin13 to LOW, PIN12 to HIGH, the others remain unchanged.
79	+	PortC.BSRR := (1 shl 13) + ((1 shl 12) shl 16);
80	+	```
81	+
82	+	### BRR - Single pin to HIGH
83	+
84	+	With this function, individual pins can be set to HIGH.
85	+
86	+	``` pascal
87	+	// Only set pin13 to HIGH, the others remain unchanged.
88	+	PortC.BSRR := 1 shl 13;
89	+	```
90	+
91	+	The upper 16 bits of BSRR correspond to the 16 bits of BRR.
92	+
93	+	## See also
94	+
95	+	- [[ARM Embedded Tutorials]] Overview
96	+
97	+	---
98	+	From the Free Pascal wiki, page "ARM Embedded Tutorial - Simple GPIO on and off output", as it stood on 2021-02-01 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
99	+	Category: ARM
100	+	Category: Embedded
101	+	Category: Tutorials

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