AVR Embedded Tutorial - Shiftregister: what changed

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Title: AVR Embedded Tutorial - Shiftregister

New		Line
1	+	# Shift Registers
2	+
3	+	The sample code is for an [ATtiny44](https://upload.chipdatas.com/root/pdf/Atmel-7701_Automotive-Microcontrollers-ATtiny24-44-84_Datasheet_eXTunT.pdf) and the shift registers used are the 74HC165 for reading and the 74HC595 for writing.
4	+
5	+	> Warning: The read routine is not compatible with Arduino shiftIn (...! The Arduino read function is for other shift registers. The clock must be controlled differently.
6	+
7	+	If you want to swap MSB to LSB, you simply have to swap downto to to.
8	+
9	+	# Port access
10	+
11	+	For how the shift register commands access the ports, see here: [[AVR Embedded Tutorial - Simple GPIO on and off output\|GPIO output]].
12	+
13	+	Do not forget to set the outputs as outputs (DDRx).
14	+
15	+	# Port constants
16	+
17	+	The pins used for the ATtiny44 and the shift register. With the AVR you can use any pins. I have declared the ports, except the data port, globally, so access from the shift registers is a little faster. If you declared them locally, everything would be more complicated because we use direct port access. Arduino does this differently, but it is about 10 times slower.
18	+
19	+	<table>
20	+	<thead>
21	+	<tr>
22	+	<th>IC</th>
23	+	<th colspan="2">Attiny44</th>
24	+	<th colspan="2">74HC165</th>
25	+	<th colspan="2">74HC595</th>
26	+	</tr>
27	+	</thead>
28	+	<tbody>
29	+	<tr>
30	+	<td></td>
31	+	<td>Pin No.</td>
32	+	<td>Description</td>
33	+	<td>Pin No.</td>
34	+	<td>Description</td>
35	+	<td>Pin No.</td>
36	+	<td>Description</td>
37	+	</tr>
38	+	<tr>
39	+	<td>dataOutPin</td>
40	+	<td>13</td>
41	+	<td>PA0</td>
42	+	<td></td>
43	+	<td></td>
44	+	<td>14</td>
45	+	<td>DS</td>
46	+	</tr>
47	+	<tr>
48	+	<td>dataInPin</td>
49	+	<td>12</td>
50	+	<td>PA1</td>
51	+	<td>10</td>
52	+	<td>DS</td>
53	+	<td></td>
54	+	<td></td>
55	+	</tr>
56	+	<tr>
57	+	<td>latchPin</td>
58	+	<td>11</td>
59	+	<td>PA2</td>
60	+	<td>1</td>
61	+	<td>PL</td>
62	+	<td>12</td>
63	+	<td>ST_CP</td>
64	+	</tr>
65	+	<tr>
66	+	<td>clockPin</td>
67	+	<td>10</td>
68	+	<td>PA3</td>
69	+	<td>2</td>
70	+	<td>CP</td>
71	+	<td>11</td>
72	+	<td>SH_CP</td>
73	+	</tr>
74	+	</tbody>
75	+	</table>
76	+
77	+	A variable is declared for the port, this has the advantage that you do not have to change all ports in the shift register functions.
78	+
79	+	``` pascal
80	+	var
81	+	shiftPORT : byte absolute PORTA;
82	+	shiftDDR : byte absolute DDRA;
83	+	shiftPIN : byte absolute PINA;
84	+	const
85	+	dataOutPin = 0;
86	+	dataInPin = 1;
87	+	latchPin = 2;
88	+	clockPin = 3;
89	+	```
90	+
91	+	# Shift register write 74HC595
92	+
93	+	``` pascal
94	+	procedure shiftOut595(val : byte);
95	+	var
96	+	i : byte;
97	+	begin
98	+	for i : = 7 downto 0 do // MSB FIRST
99	+	begin
100	+	if(val and (1 shl i)) <> 0 then
101	+	begin
102	+	shiftPORT := shiftPORT or (1 shl dataOutPin);
103	+	end
104	+	else
105	+	begin
106	+	shiftPORT := shiftPORT and not (1 shl dataOutPin);
107	+	end;
108	+
109	+	shiftPORT := shiftPORT or (1 shl clockPin);
110	+	shiftPORT := shiftPORT and not (1 shl clockPin);
111	+	end;
112	+	end;
113	+	```
114	+
115	+	# Shift register read 74HC165
116	+
117	+	``` pascal
118	+	function ShiftIn165 : byte;
119	+	var
120	+	i : byte;
121	+	begin
122	+	Result := 0;
123	+
124	+	for i := 0 to 7 do // LSB FIRST
125	+	begin
126	+	Result := (Result shl 1) or ((shiftPIN and (1 shl dataInPin)) shr dataInPin);
127	+	shiftPORT := shiftPORT or (1 shl clockPin);
128	+	shiftPORT := shiftPORT and not (1 shl clockPin);
129	+	end;
130	+	end ;
131	+	```
132	+
133	+	# Arduino shift register
134	+
135	+	This version corresponds to Arduino's shiftIn.
136	+
137	+	``` pascal
138	+	function ShiftIn : byte;
139	+	var
140	+	i : byte;
141	+	begin
142	+	Result := 0;
143	+
144	+	for i := 0 to 7 do // LSB FIRST
145	+	begin
146	+	shiftPORT := shiftPORT or (1 shl clockPin);
147	+	Result := (Result shl 1) or ((shiftPIN and (1 shl dataInPin)) shr dataInPin);
148	+	shiftPORT := shiftPORT and not (1 shl clockPin);
149	+	end;
150	+	end;
151	+	```
152	+
153	+	# Shift register examples
154	+
155	+	## Read from a shift register
156	+
157	+	Before the shift register can be read out, the port status must be written to the latch register, this is done via the LatchPin.
158	+
159	+	### Example for a 74HC165
160	+
161	+	``` pascal
162	+	var
163	+	b : byte;
164	+	begin
165	+
166	+	// Latch data
167	+	shiftPORT := shiftPORT and not (1 shl latchPin);
168	+	shiftPORT := shiftPORT or (1 shl latchPin);
169	+
170	+	// Read shift register
171	+	b := ShiftIn74HC165;
172	+	```
173	+
174	+	### Example for cascaded 74HC165
175	+
176	+	``` pascal
177	+	var
178	+	b0, bn : byte;
179	+	begin
180	+
181	+	// Latch data
182	+	shiftPORT := shiftPORT and not (1 shl latchPin);
183	+	shiftPORT := shiftPORT or (1 shl latchPin);
184	+
185	+	// Read shift register
186	+	b0 := ShiftIn74HC165;
187	+
188	+	// ...
189	+
190	+	bn := ShiftIn74HC165;
191	+	```
192	+
193	+	## Write to a shift register
194	+
195	+	If the data is written into the shift register, you have to add the latch clock that the current outputs become active.
196	+
197	+	### Example for a 74HC595
198	+
199	+	``` pascal
200	+	var
201	+	b : byte;
202	+	begin
203	+	b := 123;
204	+
205	+	// Write shift register
206	+	shiftOut595(b);
207	+
208	+	// Latch data
209	+	shiftPORT := shiftPORT and not (1 shl latchPin);
210	+	shiftPORT := shiftPORT or (1 shl latchPin);
211	+	```
212	+
213	+	### Example for cascaded 74HC595
214	+
215	+	``` pascal
216	+	var
217	+	b0, bn : byte;
218	+	begin
219	+	b0 := 123;
220	+
221	+	// ...
222	+
223	+	bn := 789;
224	+
225	+	// Write shift register
226	+	shiftOut595(b0);
227	+
228	+	// ...
229	+
230	+	shiftOut595(bn);
231	+
232	+	// Latch data
233	+	shiftPORT := shiftPORT and not (1 shl latchPin);
234	+	shiftPORT := shiftPORT or (1 shl latchPin);
235	+	```
236	+
237	+	# See also
238	+
239	+	- [[AVR Embedded Tutorial\|AVR Embedded Tutorials]] - Overview
240	+	- [[AVR Embedded Tutorial - SPI Shiftregister\|SPI shift register]] - control shift register 74HC595 via SPI (very fast).
241	+
242	+	---
243	+	From the Free Pascal wiki, page "AVR Embedded Tutorial - Shiftregister", as it stood on 2023-08-02 after a change by Zave2023, 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).
244	+	Category: AVR
245	+	Category: Arduino
246	+	Category: Embedded
247	+	Category: Tutorials

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