// 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(const machine_config &mconfig, std::string 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 (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; }