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// license:BSD-3-Clause
// copyright-holders:hap
/*
National Semiconductor DS8874 9-Digit Shift Input LED Driver
It's basically a 9-bit generic shifter, outputs are active-low.
Only one output is active at a time.
TODO:
- add 1-bit callbacks/read functions if necessary
- datasheet info is very sparse, so implementation may have errors
- low battery pin
*/
#include "emu.h"
#include "machine/ds8874.h"
DEFINE_DEVICE_TYPE(DS8874, ds8874_device, "ds8874", "DS8874 LED Driver")
//-------------------------------------------------
// constructor
//-------------------------------------------------
ds8874_device::ds8874_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock) :
device_t(mconfig, DS8874, tag, owner, clock),
m_write_output(*this)
{ }
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void ds8874_device::device_start()
{
// zerofill
m_data = 0;
m_cp = 0;
m_shift = 0xff;
// register for savestates
save_item(NAME(m_data));
save_item(NAME(m_cp));
save_item(NAME(m_shift));
}
//-------------------------------------------------
// handlers
//-------------------------------------------------
void ds8874_device::refresh_output()
{
m_write_output(m_shift);
}
void ds8874_device::data_w(int state)
{
state = (state) ? 1 : 0;
// reset shift register at falling edge
if (!state && m_data)
{
m_shift = 0x1fe;
refresh_output();
}
m_data = state;
}
void ds8874_device::cp_w(int state)
{
state = (state) ? 1 : 0;
// clock shift register at any edge
if (state != m_cp && m_shift != 0xff)
{
m_shift = (m_shift << 1 & 0x1ff) | 1;
refresh_output();
}
m_cp = state;
}
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