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diff --git a/src/devices/machine/74148.cpp b/src/devices/machine/74148.cpp
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+// 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 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 (int i = 0; i < 8; i++)
+ m_input_lines[i] = 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;
+}