AVR Embedded Tutorial - I²C EEPROM: what changed

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Title: AVR Embedded Tutorial - I²C EEPROM

New		Line
1	+	# I²C EEPROM (24LC256)
2	+
3	+	This code is for an Atmega328 / Arduino with a 16MHz clock and an [24LC256](https://www.microchip.com/wwwproducts/en/24LC256) I2C compatible 2-wire Serial EEPROM. Other 24LCxx EEPROMs can also be controlled.
4	+
5	+	The following functions are described in other tutorials:
6	+
7	+	- [[AVR Embedded Tutorial - Delays\|Delays]]
8	+	- [[AVR Embedded Tutorial - UART\|UART - serial interface]]
9	+	- [[AVR Embedded Tutorial - I²C, TWI\|Activate I²C bus]] or [[AVR Embedded Tutorial - Software I2C, TWI]]
10	+
11	+	This tutorial shows you how to control an external EEPROM (24LC256) which is connected to the I²C bus.
12	+
13	+	PullUp resistors are necessary, the EEPROM does not contain any itself.
14	+
15	+	## Functions for EEPROM (24LC256) control
16	+
17	+	### Constants
18	+
19	+	``` pascal
20	+	const
21	+	TWI_Write = 0;
22	+	TWI_Read = 1;
23	+	```
24	+
25	+	### Functions
26	+
27	+	Note: For a [[Shortstring\|ShortString]], the length byte is stored at position \[0\] in the string.
28	+
29	+	Call parameters:
30	+
31	+	- addr device address on the I²C bus
32	+	- pos storage location in the EEPROM
33	+	- value byte to be written
34	+
35	+	#### Functions for writing and reading a byte
36	+
37	+	``` pascal
38	+	// Write a character
39	+	procedure I2C_EEPROM_Write(addr , pos : Int16; value : Byte);
40	+	begin
41	+	TWIStart((addr shl 1) or TWI_Write);
42	+	TWIWrite(pos shr 8);
43	+	TWIWrite(pos and $FF);
44	+	TWIWrite(value);
45	+	TWIStop;
46	+	delay_ms(10);
47	+	end;
48	+
49	+	// Read a character
50	+	function I2C_EEPROM_Read(addr, pos : Int16) : byte;
51	+	begin
52	+	TWIStart((addr shl 1) or TWI_Write);
53	+	TWIWrite(pos shr 8);
54	+	TWIWrite(pos and $FF);
55	+	TWIStop;
56	+
57	+	TWIStart((addr shl 1) or TWI_Read);
58	+	Result := TWIReadNACK;
59	+	TWIStop;
60	+	end;
61	+	```
62	+
63	+	#### Functions for writing and reading a string
64	+
65	+	A [[Shortstring\|ShortString]], or other buffer, is written / read character by character.
66	+
67	+	``` pascal
68	+	// Write a string, including length byte
69	+	procedure I2C_EEPROM_WriteString(addr, pos : Int16; s : ShortString);
70	+	var
71	+	i : byte;
72	+	begin
73	+	for i := 0 to Length(s) do
74	+	begin
75	+	I2C_EEPROM_Write(addr, pos + i, byte(s[i]));
76	+	end;
77	+	end;
78	+
79	+	// Read a string, including length byte
80	+	function I2C_EEPROM_ReadString(addr, pos : Int16) : ShortString;
81	+	var
82	+	i, l : byte;
83	+	begin
84	+	l := I2C_EEPROM_Read(addr, pos); // read length of string stored at [0]
85	+	SetLength(Result, l);
86	+	for i := 1 to l do
87	+	begin
88	+	Result[i] := Char(I2C_EEPROM_Read(addr, pos + i));
89	+	end;
90	+	end;
91	+	```
92	+
93	+	## Example program
94	+
95	+	### Constants and variables
96	+
97	+	``` pascal
98	+	const
99	+	I2Caddr = $54; // Address of the 24LC256 on the I²C bus
100	+	s1 = 'Hello World!';
101	+	s2 = 'AVR with Lazarus is so beautiful';
102	+
103	+	var
104	+	s : ShortString;
105	+	```
106	+
107	+	### Main program
108	+
109	+	Since a [[Shortstring\|ShortString]] is 256 bytes long, the second string at address \$100 (256) is saved in the EEPROM.
110	+
111	+	``` pascal
112	+	begin
113	+	UARTInit; // initialize UART
114	+	TWIInit; // initialize I²C
115	+	asm Sei end; // enable interrupts
116	+
117	+	// save the two strings
118	+	I2C_EEPROM_WriteString(I2Caddr, 0, s1); // first string
119	+	I2C_EEPROM_WriteString(I2Caddr, $100, s2); // second string
120	+
121	+	// eeload the strings for verification
122	+	repeat
123	+	s := I2C_EEPROM_ReadString(I2Caddr, 0);
124	+	UARTSendString('s1:');
125	+	UARTSendString(s);
126	+	UARTSendString(#13#10);
127	+
128	+	s := I2C_EEPROM_ReadString(I2Caddr, $100);
129	+	UARTSendString('s2:');
130	+	UARTSendString(s);
131	+	UARTSendString(#13#10);
132	+	until 1 = 2;
133	+	end.
134	+	```
135	+
136	+	If you do not believe that the string is in the EEPROM, you can exclude the two lines with WriteString (... and test again.
137	+
138	+	# See also
139	+
140	+	- Overview page - [[AVR Embedded Tutorial\|AVR Embedded Tutorials]]
141	+
142	+	---
143	+	From the Free Pascal wiki, page "AVR Embedded Tutorial - I²C EEPROM", as it stood on 2020-03-08 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).

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