// license:BSD-3-Clause // copyright-holders:AJR /********************************************************************** National Semiconductor ADC0804 8-bit µP Compatible A/D Converter The ADC0804 is the most widely used member of a family of five CMOS 8-bit ADCs with microprocessor-compatible interfaces, which differ from each other only in error specifications: ADC0801 ±¼ LSB Full-scale adjusted ADC0802 ±½ LSB Vref/2 = 2.500 Vdc ADC0803 ±½ LSB Full-scale adjusted ADC0804 ±1 LSB Vref/2 = 2.500 Vdc ADC0805 ±1 LSB Vref/2 = NC Though these devices are designed to convert differential analog inputs, single-phase conversion can be achieved by tying pin 7 (negative Vin) to pin 8 (analog GND). A CD4051B or other analog switch IC is often used to multiplex several input sources. Pin 4 should be connected to either an externally generated clock signal (640 kHz typical, 1460 kHz maximum) or a timing capacitor plus a resistor bridged to pin 19. The resistor is typically 10 kΩ but higher values may be needed due to loading conditions when multiple other devices are also clocked through pin 19, which yields the output of the internal Schmitt trigger clock circuit. The ADC0804's INTR semaphore output reflects not the actual busy state of the converter (as EOC does on the ADC0808) but an internal flip-flop attached to it. This flip-flop is reset by pulling either RD or WR active low; therefore, INTR will never toggle if RD is tied to GND to keep the data outputs continuously active. **********************************************************************/ #include "emu.h" #include "adc0804.h" //************************************************************************** // TYPE DEFINITIONS //************************************************************************** DEFINE_DEVICE_TYPE(ADC0803, adc0803_device, "adc0803", "ADC0803 A/D Converter") DEFINE_DEVICE_TYPE(ADC0804, adc0804_device, "adc0804", "ADC0804 A/D Converter") ALLOW_SAVE_TYPE(adc0804_device::read_mode); //************************************************************************** // DEVICE CONSTRUCTION AND INITIALIZATION //************************************************************************** //------------------------------------------------- // adc0804_device - constructor //------------------------------------------------- adc0804_device::adc0804_device(const machine_config &mconfig, device_type type, const char *tag, device_t *owner, u32 clock) : device_t(mconfig, type, tag, owner, clock) , m_vin_callback(*this, 0) , m_intr_callback(*this) , m_res(0.0) , m_cap(0.0) , m_fclk_rc(attotime::zero) , m_timer(nullptr) , m_rd_mode(RD_STROBED) , m_rd_active(false) , m_wr_active(false) , m_result(0) , m_intr_active(false) { } adc0804_device::adc0804_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock) : adc0804_device(mconfig, ADC0804, tag, owner, clock) { } //------------------------------------------------- // adc0803_device - constructor //------------------------------------------------- adc0803_device::adc0803_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock) : adc0804_device(mconfig, ADC0803, tag, owner, clock) { } //------------------------------------------------- // device_resolve_objects - resolve objects that // may be needed for other devices to set // initial conditions at start time //------------------------------------------------- void adc0804_device::device_resolve_objects() { if (m_rd_mode == RD_GROUNDED) m_rd_active = true; } //------------------------------------------------- // device_start - device-specific startup //------------------------------------------------- void adc0804_device::device_start() { // calculate RC timing if (m_res == 0.0 || m_cap == 0.0) m_fclk_rc = attotime::zero; else m_fclk_rc = attotime::from_double(m_res * m_cap / 1.1); // create timer m_timer = timer_alloc(FUNC(adc0804_device::conversion_done), this); // save state if (m_rd_mode == RD_BITBANGED) save_item(NAME(m_rd_active)); save_item(NAME(m_wr_active)); save_item(NAME(m_result)); save_item(NAME(m_intr_active)); } //************************************************************************** // CONVERSION SEQUENCE //************************************************************************** // Conversion occurs over a busy period of 66–73 cycles, after 1–8 cycles of latency const int adc0804_device::s_conversion_cycles = 74; //------------------------------------------------- // set_interrupt - set or clear INTR output //------------------------------------------------- void adc0804_device::set_interrupt(bool state) { if (m_intr_active != state) { m_intr_active = state; m_intr_callback(state ? ASSERT_LINE : CLEAR_LINE); } } //------------------------------------------------- // conversion_start - begin the busy period //------------------------------------------------- void adc0804_device::conversion_start() { if (!m_timer->enabled()) m_timer->adjust(m_fclk_rc != attotime::zero ? m_fclk_rc * s_conversion_cycles : clocks_to_attotime(s_conversion_cycles)); else logerror("%s: Tried to start conversion when already in progress\n", machine().describe_context()); } //------------------------------------------------- // conversion_done - load result and signal // interrupt //------------------------------------------------- TIMER_CALLBACK_MEMBER(adc0804_device::conversion_done) { m_result = m_vin_callback(); if (!m_rd_active && !m_wr_active) set_interrupt(true); } //************************************************************************** // BUS INTERFACE //************************************************************************** //------------------------------------------------- // read - read the 8-bit conversion result //------------------------------------------------- u8 adc0804_device::read() { switch (m_rd_mode) { case RD_STROBED: if (!machine().side_effects_disabled()) set_interrupt(false); break; case RD_BITBANGED: if (!m_rd_active) return 0xff; // open bus break; case RD_GROUNDED: break; } return m_result; } //------------------------------------------------- // write - begin a new conversion //------------------------------------------------- void adc0804_device::write(u8 data) { // data is ignored set_interrupt(false); conversion_start(); } //------------------------------------------------- // read_and_write - read the result of the last // conversion and begin a new one //------------------------------------------------- u8 adc0804_device::read_and_write() { if (!machine().side_effects_disabled()) { set_interrupt(false); conversion_start(); } if (m_rd_mode == RD_BITBANGED && !m_rd_active) return 0xff; // open bus else return m_result; } //------------------------------------------------- // rd_w - enable data bus by line write //------------------------------------------------- void adc0804_device::rd_w(int state) { assert(m_rd_mode == RD_BITBANGED); // RD input is active low if (!state && !m_rd_active) { m_rd_active = true; set_interrupt(false); } else if (state && m_rd_active) m_rd_active = false; } //------------------------------------------------- // wr_w - begin conversion by line write //------------------------------------------------- void adc0804_device::wr_w(int state) { // WR input is active low if (!state && !m_wr_active) { m_wr_active = true; set_interrupt(false); } else if (state && m_wr_active) { m_wr_active = false; conversion_start(); } }