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Chips de la serie 74
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Contenido
Introduction
History: a computer from the catalogue
Lesson 0. Gates from transistors: for those who start from scratch
0.1. The idea: a transistor is a switch
0.2. Building
0.3. Check
Lesson 0 paste (Cmd+I)
Lesson 1. Logic in packages: 74HC00, 02, 04, 08, 32
1.1. The idea: a chip is a package with gates
1.2. The idea: free inputs go to ground
1.3. The idea: a latch from one chip
1.4. Building
1.5. Check
Lesson 1 paste (Cmd+I)
Lesson 2. Flip-flops in a package: 74HC74 and a frequency divider
2.1. The idea: a flip-flop with set and reset
2.2. The idea: six NANDs inside
2.3. The idea: a divider is a flip-flop that flips
2.4. Building
2.5. Check
Lesson 2 paste (Cmd+I)
Lesson 3. A counter in a package: 74HC390 and a stopwatch
3.1. The idea: ÷2 and ÷5 make ÷10
3.2. The idea: clocking on the fall
3.3. The idea: reset on a one
3.4. Building
3.5. Check
Lesson 3 paste (Cmd+I)
Lesson 4. A decoder in a package: 74HC138 and a running light
4.1. The idea: number → one wire
4.2. The idea: active 0
4.3. The idea: 4 → 16 from two 3 → 8
4.4. Building
4.5. Check
Lesson 4 paste (Cmd+I)
Lesson 5. A shift register: 74HC595 and 8 lamps over three wires
5.1. The idea: bits over one wire
5.2. The idea: a latch shows everything at once
5.3. The idea: the third state
5.4. Building
5.5. Check
Lesson 5 paste (Cmd+I)
Lesson 6. Bus buffers: 74HC244 and 74HC245
6.1. The idea: a bus and the third state
6.2. The idea: a buffer is a double inversion
6.3. The idea: both ways — two 74HC244
6.4. Building
6.5. Check
Lesson 6 paste (Cmd+I)
Lesson 7. An electronic dice
7.1. The idea: a counter to six
7.2. The idea: face number → dots
7.3. The idea: a fair roll
7.4. Building
7.5. Check
Lesson 7 paste (Cmd+I)
Summary
All the parts
Instructions in pictures
Lesson 6 in pictures
← Back to the lesson: Lesson 6. Bus buffers: 74HC244 and 74HC245
6
Bus buffers
74HC244 and 74HC245: shared wires — only one talks
kh
HB-05
74HC244
74HC245
IN
20×
OUT
16×
74HC04
5×
1
TG
8×
74HC00
1×
1
0
15×
74HC32
1×
1
16×
4b
0
A
1×
4×
∞
Ctrl
+
G
74HC244
74HC245
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS
1
Delete
0
DATA
Shift
Shift
SH
Latch
Latch
ST
Clear
Clear
CLRB
0
OFF
L0
GND
L1
GND
L2
GND
L3
GND
2
Delete
L4
GND
L5
GND
L6
GND
L7
GND
L0
L1
L2
L3
L4
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS …
3
Delete
L5
L6
L7
SO
4
Delete
74HC04
1A
CLRB
2A
GND
3A
GND
4A
GND
5A
GND
6A
GND
1Y
nCLRB
2Y
3Y
4Y
5Y
6Y
74HC595
MR
nCLRB
SHCP
SH
STCP
ST
OE
OFF
DS
DATA
Q1
L1
Q2
L2
Q3
L3
Q4
L4
Q5
L5
Q6
L6
Q7
L7
Q0
L0
Q7S
SO
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC244
5
IN
10×
OUT
8×
1OE
1A0
1A1
1A2
1A3
2A3
2A2
2A1
2A0
2OE
2Y0
2Y1
2Y2
2Y3
1Y3
1Y2
1Y1
1Y0
6
74HC04
1×
1
12×
74HC04
1A
1A0
2A
1A1
3A
1A2
4A
1A3
5A
2A0
6A
2A1
1Y
n1A0
2Y
n1A1
3Y
n1A2
4Y
n1A3
5Y
n2A0
6Y
n2A1
7
74HC04
1×
1
12×
74HC04
1A
2A2
2A
2A3
3A
n1A0
4A
n1A1
5A
n1A2
6A
n1A3
1Y
n2A2
2Y
n2A3
3Y
b1A0
4Y
b1A1
5Y
b1A2
6Y
b1A3
8
74HC04
1×
1
12×
74HC04
1A
n2A0
2A
n2A1
3A
n2A2
4A
n2A3
5A
1OE
6A
2OE
1Y
b2A0
2Y
b2A1
3Y
b2A2
4Y
b2A3
5Y
e1
6Y
e2
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC244 …
9
TG
3×
9×
Transmission gate
A
b1A0
EN
e1
B
1Y0
Transmission gate
A
b1A1
EN
e1
B
1Y1
Transmission gate
A
b1A2
EN
e1
B
1Y2
10
TG
3×
9×
Transmission gate
A
b1A3
EN
e1
B
1Y3
Transmission gate
A
b2A0
EN
e2
B
2Y0
Transmission gate
A
b2A1
EN
e2
B
2Y1
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC244 …
11
TG
2×
6×
Transmission gate
A
b2A2
EN
e2
B
2Y2
Transmission gate
A
b2A3
EN
e2
B
2Y3
12
Ctrl
+
G
Library
…
Chip N
2×
Library
…
74HC244
Enter
74HC244
1OE
1A0
1A1
1A2
1A3
2A3
2A2
2A1
2A0
2OE
2Y0
2Y1
2Y2
2Y3
1Y3
1Y2
1Y1
1Y0
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC245
13
IN
10×
OUT
8×
DIR
A0
A1
A2
A3
A4
A5
A6
A7
OE
B7
B6
B5
B4
B3
B2
B1
B0
14
74HC04
1×
1
8×
74HC04
1A
OE
2A
DIR
3A
GND
4A
GND
5A
GND
6A
GND
1Y
nOE
2Y
nDIR
3Y
4Y
5Y
6Y
15
74HC00
1×
1
10×
74HC00
1A
nOE
1B
DIR
2A
nOE
2B
nDIR
3A
GND
3B
GND
4A
GND
4B
GND
1Y
oAB
2Y
oBA
3Y
4Y
16
74HC244
1×
18×
74HC244
1OE
oAB
1A0
A0
1A1
A1
1A2
A2
1A3
A3
2A3
A7
2A2
A6
2A1
A5
2A0
A4
2OE
oAB
2Y0
B4
2Y1
B5
2Y2
B6
2Y3
B7
1Y3
B3
1Y2
B2
1Y1
B1
1Y0
B0
© 2026 Daniil Khanin · khanin.info · HB-05
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74HC245 …
17
74HC244
1×
18×
74HC244
1OE
oBA
1A0
B0
1A1
B1
1A2
B2
1A3
B3
2A3
B7
2A2
B6
2A1
B5
2A0
B4
2OE
oBA
2Y0
A4
2Y1
A5
2Y2
A6
2Y3
A7
1Y3
A3
1Y2
A2
1Y1
A1
1Y0
A0
18
Ctrl
+
G
Library
…
Chip N
2×
Library
…
74HC245
Enter
74HC245
DIR
A0
A1
A2
A3
A4
A5
A6
A7
OE
B7
B6
B5
B4
B3
B2
B1
B0
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS
19
0
5×
5×
0
X0
0
X1
0
X2
0
X3
0
Y0
20
0
3×
3×
0
Y1
0
Y2
0
Y3
21
0
2×
2×
0
SEL
0
OFF
22
74HC04
1×
1
7×
74HC04
1A
SEL
2A
GND
3A
GND
4A
GND
5A
GND
6A
GND
1Y
nSEL
2Y
3Y
4Y
5Y
6Y
23
74HC32
1×
1
10×
74HC32
1A
SEL
1B
OFF
2A
nSEL
2B
OFF
3A
GND
3B
GND
4A
GND
4B
GND
1Y
oeX
2Y
oeY
3Y
4Y
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS …
24
74HC244
1×
18×
74HC244
1OE
oeX
1A0
X0
1A1
X1
1A2
X2
1A3
X3
2A3
Y3
2A2
Y2
2A1
Y1
2A0
Y0
2OE
oeY
2Y0
BUS0
2Y1
BUS1
2Y2
BUS2
2Y3
BUS3
1Y3
BUS3
1Y2
BUS2
1Y1
BUS1
1Y0
BUS0
25
3×
6×
BUS0
GND
BUS1
GND
BUS2
GND
26
1×
2×
BUS3
GND
© 2026 Daniil Khanin · khanin.info · HB-05
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CANVAS …
27
0
5×
5×
0
DIR
0
KS0
0
KS1
0
KS2
0
KS3
28
3×
6×
KS0
K0
KS1
K1
KS2
K2
29
1×
2×
KS3
K3
30
74HC245
1×
18×
74HC245
DIR
DIR
A0
BUS0
A1
BUS1
A2
BUS2
A3
BUS3
A4
UA4
A5
UA5
A6
UA6
A7
UA7
OE
GND
B7
UB7
B6
UB6
B5
UB5
B4
UB4
B3
K3
B2
K2
B1
K1
B0
K0
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CANVAS …
31
3×
6×
UA4
GND
UA5
GND
UA6
GND
32
3×
6×
UA7
GND
UB4
GND
UB5
GND
33
2×
4×
UB6
GND
UB7
GND
34
4b
0
A
1×
4×
4×
4b
0
BUS
K0
K1
K2
K3
0
SEL
SEL = 0 → X, SEL = 1 → Y
© 2026 Daniil Khanin · khanin.info · HB-05
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← Back to the lesson
Lesson 6. Bus buffers: 74HC244 and 74HC245