summaryrefslogtreecommitdiffstatshomepage
path: root/src/devices/machine/74148.cpp
blob: 8786d2aa7b4c15c8a0ccf380aa7c753f0f4694ed (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
// license:BSD-3-Clause
// copyright-holders:Aaron Giles
/*****************************************************************************

  74148 8-line-to-3-line priority encoder


  Pin layout and functions to access pins:

  input_line_w(4)  [1] /IN4   VCC [16]
  input_line_w(5)  [2] /IN5   /EO [15]  enable_output_r
  input_line_w(6)  [3] /IN6   /GS [14]  output_valid_r
  input_line_w(7)  [4] /IN7  /IN3 [13]  input_line_w(3)
  enable_input_w   [5] /EI   /IN2 [12]  input_line_w(2)
  output_r         [6] /A2   /IN1 [11]  input_line_w(1)
  output_r         [7] /A1   /IN0 [10]  input_line_w(0)
                   [8] GND   /A0  [9]   output_r


  Truth table (all logic levels indicate the actual voltage on the line):

              INPUTS            |     OUTPUTS
                                |
    EI  I0 I1 I2 I3 I4 I5 I6 I7 | A2 A1 A0 | GS EO
    ----------------------------+----------+------
 1  H   X  X  X  X  X  X  X  X  | H  H  H  | H  H
 2  L   H  H  H  H  H  H  H  H  | H  H  H  | H  L
 3  L   X  X  X  X  X  X  X  L  | L  L  L  | L  H
 4  L   X  X  X  X  X  X  L  H  | L  L  H  | L  H
 5  L   X  X  X  X  X  L  H  H  | L  H  L  | L  H
 6  L   X  X  X  X  L  H  H  H  | L  H  H  | L  H
 7  L   X  X  X  L  H  H  H  H  | H  L  L  | L  H
 8  L   X  X  L  H  H  H  H  H  | H  L  H  | L  H
 9  L   X  L  H  H  H  H  H  H  | H  H  L  | L  H
 10 L   L  H  H  H  H  H  H  H  | H  H  H  | L  H
    ----------------------------+----------+------
    L   = lo (0)
    H   = hi (1)
    X   = any state

*****************************************************************************/

#include "emu.h"
#include "machine/74148.h"


const device_type TTL74148 = &device_creator<ttl74148_device>;

ttl74148_device::ttl74148_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
				: device_t(mconfig, TTL74148, "74148 TTL", tag, owner, clock, "74148", __FILE__),
					m_enable_input(0),
					m_output(0),
					m_output_valid(0),
					m_enable_output(0),
					m_last_output(0),
					m_last_output_valid(0),
					m_last_enable_output(0)
{
	for (auto & elem : m_input_lines)
		elem = 0;
}

//-------------------------------------------------
//  device_start - device-specific startup
//-------------------------------------------------

void ttl74148_device::device_start()
{
	m_output_cb.bind_relative_to(*owner());

	save_item(NAME(m_input_lines));
	save_item(NAME(m_enable_input));
	save_item(NAME(m_output));
	save_item(NAME(m_output_valid));
	save_item(NAME(m_enable_output));
	save_item(NAME(m_last_output));
	save_item(NAME(m_last_output_valid));
	save_item(NAME(m_last_enable_output));
}

//-------------------------------------------------
//  device_reset - device-specific reset
//-------------------------------------------------

void ttl74148_device::device_reset()
{
	m_enable_input = 1;
	m_input_lines[0] = 1;
	m_input_lines[1] = 1;
	m_input_lines[2] = 1;
	m_input_lines[3] = 1;
	m_input_lines[4] = 1;
	m_input_lines[5] = 1;
	m_input_lines[6] = 1;
	m_input_lines[7] = 1;

	m_last_output = -1;
	m_last_output_valid = -1;
	m_last_enable_output = -1;
}


void ttl74148_device::update()
{
	if (m_enable_input)
	{
		// row 1 in truth table
		m_output = 0x07;
		m_output_valid = 1;
		m_enable_output = 1;
	}
	else
	{
		int bit0, bit1, bit2;

		/* this comes straight off the data sheet schematics */
		bit0 = !(((!m_input_lines[1]) &
					m_input_lines[2] &
					m_input_lines[4] &
					m_input_lines[6])  |
					((!m_input_lines[3]) &
					m_input_lines[4] &
					m_input_lines[6])  |
					((!m_input_lines[5]) &
					m_input_lines[6])  |
					(!m_input_lines[7]));

		bit1 = !(((!m_input_lines[2]) &
					m_input_lines[4] &
					m_input_lines[5])  |
					((!m_input_lines[3]) &
					m_input_lines[4] &
					m_input_lines[5])  |
					(!m_input_lines[6])  |
					(!m_input_lines[7]));

		bit2 = !((!m_input_lines[4])  |
					(!m_input_lines[5])  |
					(!m_input_lines[6])  |
					(!m_input_lines[7]));

		m_output = (bit2 << 2) | (bit1 << 1) | bit0;

		m_output_valid = (m_input_lines[0] &
										m_input_lines[1] &
										m_input_lines[2] &
										m_input_lines[3] &
										m_input_lines[4] &
										m_input_lines[5] &
										m_input_lines[6] &
										m_input_lines[7]);

		m_enable_output = !m_output_valid;
	}


	/* call callback if any of the outputs changed */
	if (!m_output_cb.isnull() &&
		((m_output != m_last_output) ||
			(m_output_valid != m_last_output_valid) || (m_enable_output != m_last_enable_output)))
	{
		m_last_output = m_output;
		m_last_output_valid = m_output_valid;
		m_last_enable_output = m_enable_output;

		m_output_cb();
	}
}


void ttl74148_device::input_line_w(int input_line, int data)
{
	m_input_lines[input_line] = data ? 1 : 0;
}


void ttl74148_device::enable_input_w(int data)
{
	m_enable_input = data ? 1 : 0;
}


int ttl74148_device::output_r()
{
	return m_output;
}


int ttl74148_device::output_valid_r()
{
	return m_output_valid;
}


int ttl74148_device::enable_output_r()
{
	return m_enable_output;
}