summaryrefslogtreecommitdiffstatshomepage
path: root/src/emu/machine/74148.c
blob: 856ab3cd2774d47417a6c9367dfc32cd7646157c (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
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
/*****************************************************************************

  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"


typedef struct _ttl74148_state ttl74148_state;
struct _ttl74148_state
{
	/* callback */
	void (*output_cb)(device_t *device);

	/* inputs */
	int input_lines[8];	/* pins 1-4,10-13 */
	int enable_input;	/* pin 5 */

	/* outputs */
	int output;			/* pins 6,7,9 */
	int output_valid;	/* pin 14 */
	int enable_output;	/* pin 15 */

	/* internals */
	int last_output;
	int last_output_valid;
	int last_enable_output;
};


INLINE ttl74148_state *get_safe_token(device_t *device)
{
	assert(device != NULL);
	assert(device->type() == TTL74148);

	return (ttl74148_state *)downcast<legacy_device_base *>(device)->token();
}

void ttl74148_update(device_t *device)
{
	ttl74148_state *state = get_safe_token(device);

	if (state->enable_input)
	{
		// row 1 in truth table
		state->output = 0x07;
		state->output_valid = 1;
		state->enable_output = 1;
	}
	else
	{
		int bit0, bit1, bit2;

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

		bit1 = !(((!state->input_lines[2]) &
		           state->input_lines[4] &
		           state->input_lines[5])  |
		         ((!state->input_lines[3]) &
		           state->input_lines[4] &
		           state->input_lines[5])  |
		         (!state->input_lines[6])  |
		         (!state->input_lines[7]));

		bit2 = !((!state->input_lines[4])  |
		         (!state->input_lines[5])  |
		         (!state->input_lines[6])  |
		         (!state->input_lines[7]));

		state->output = (bit2 << 2) | (bit1 << 1) | bit0;

		state->output_valid = (state->input_lines[0] &
									 state->input_lines[1] &
									 state->input_lines[2] &
									 state->input_lines[3] &
									 state->input_lines[4] &
									 state->input_lines[5] &
									 state->input_lines[6] &
									 state->input_lines[7]);

		state->enable_output = !state->output_valid;
	}


	/* call callback if any of the outputs changed */
	if (  state->output_cb &&
		((state->output        != state->last_output) ||
	     (state->output_valid  != state->last_output_valid) ||
	     (state->enable_output != state->last_enable_output)))
	{
		state->last_output = state->output;
		state->last_output_valid = state->output_valid;
		state->last_enable_output = state->enable_output;

		state->output_cb(device);
	}
}


void ttl74148_input_line_w(device_t *device, int input_line, int data)
{
	ttl74148_state *state = get_safe_token(device);
	state->input_lines[input_line] = data ? 1 : 0;
}


void ttl74148_enable_input_w(device_t *device, int data)
{
	ttl74148_state *state = get_safe_token(device);
	state->enable_input = data ? 1 : 0;
}


int ttl74148_output_r(device_t *device)
{
	ttl74148_state *state = get_safe_token(device);
	return state->output;
}


int ttl74148_output_valid_r(device_t *device)
{
	ttl74148_state *state = get_safe_token(device);
	return state->output_valid;
}


int ttl74148_enable_output_r(device_t *device)
{
	ttl74148_state *state = get_safe_token(device);
	return state->enable_output;
}


static DEVICE_START( ttl74148 )
{
	ttl74148_config *config = (ttl74148_config *)device->static_config();
	ttl74148_state *state = get_safe_token(device);
    state->output_cb = config->output_cb;

    device->save_item(NAME(state->input_lines));
    device->save_item(NAME(state->enable_input));
    device->save_item(NAME(state->output));
    device->save_item(NAME(state->output_valid));
    device->save_item(NAME(state->enable_output));
    device->save_item(NAME(state->last_output));
    device->save_item(NAME(state->last_output_valid));
    device->save_item(NAME(state->last_enable_output));
}


static DEVICE_RESET( ttl74148 )
{
	ttl74148_state *state = get_safe_token(device);

    state->enable_input = 1;
    state->input_lines[0] = 1;
    state->input_lines[1] = 1;
    state->input_lines[2] = 1;
    state->input_lines[3] = 1;
    state->input_lines[4] = 1;
    state->input_lines[5] = 1;
    state->input_lines[6] = 1;
    state->input_lines[7] = 1;

    state->last_output = -1;
    state->last_output_valid = -1;
    state->last_enable_output = -1;
}


DEVICE_GET_INFO(ttl74148)
{
 switch (state)
 {
  case DEVINFO_INT_TOKEN_BYTES: info->i = sizeof(ttl74148_state); break;

  case DEVINFO_FCT_START: info->start = DEVICE_START_NAME(ttl74148); break;

  case DEVINFO_FCT_RESET: info->reset = DEVICE_RESET_NAME(ttl74148); break;

  case DEVINFO_STR_NAME: strcpy(info->s, "74148"); break;
 }
}

DEFINE_LEGACY_DEVICE(TTL74148, ttl74148);