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// license:BSD-3-Clause
// copyright-holders:Fabio Priuli
/**********************************************************************
Sega Master System "Graphic Board" emulation
I/O 3f write | this method
0x20 | 0x7f
0x00 | 0x3f
0x30 | 0xff
Typical sequence:
- 3f write 0x20
- read dc
- 3f write 0x00
- read dc
- 3f write 0x20
- read dc
- 3f write 0x30
Suspect from kind of counter that is reset by a 0x30 write to I/O port 0x3f.
Once reset reads from i/O port dc expect to see 0xE0.
And then any write with differing bits goes through several internal I/O ports
with the first port being the one with the buttons
In the reset/start state the lower four/five bits are 0.
Then a nibble is read containing the buttons (active low)
Then 2 nibbles are read to form a byte (first high nibble, then low nibble) indicating
whether the pen is on the graphic board, a value of FD, FE, or FF used for this. For
any other value the following 2 bytes are not read.
Then 2 nibbles are read to form a byte containing the absolute X coordinate.
Then 2 nibbles are read to form a byte containing the absolute Y coordiante.
**********************************************************************/
#include "emu.h"
#include "graphic.h"
//**************************************************************************
// DEVICE DEFINITIONS
//**************************************************************************
DEFINE_DEVICE_TYPE(SMS_GRAPHIC, sms_graphic_device, "sms_graphic", "Sega SMS Graphic Board")
static INPUT_PORTS_START( sms_graphic )
PORT_START("BUTTONS")
PORT_BIT( 0x01, IP_ACTIVE_LOW, IPT_BUTTON1 ) // MENU
PORT_BIT( 0x02, IP_ACTIVE_LOW, IPT_BUTTON2 ) // DO
PORT_BIT( 0x04, IP_ACTIVE_LOW, IPT_BUTTON3 ) // PEN
PORT_BIT( 0xf8, IP_ACTIVE_LOW, IPT_UNUSED )
PORT_START("X")
PORT_BIT( 0xff, 0x00, IPT_LIGHTGUN_X) PORT_CROSSHAIR(X, 1.0, 0.0, 0) PORT_SENSITIVITY(50) PORT_KEYDELTA(15)
PORT_START("Y")
PORT_BIT( 0xff, 0x00, IPT_LIGHTGUN_Y) PORT_CROSSHAIR(Y, 1.0, 0.0, 0) PORT_SENSITIVITY(50) PORT_KEYDELTA(15)
INPUT_PORTS_END
//-------------------------------------------------
// input_ports - device-specific input ports
//-------------------------------------------------
ioport_constructor sms_graphic_device::device_input_ports() const
{
return INPUT_PORTS_NAME( sms_graphic );
}
//**************************************************************************
// LIVE DEVICE
//**************************************************************************
//-------------------------------------------------
// sms_graphic_device - constructor
//-------------------------------------------------
sms_graphic_device::sms_graphic_device(const machine_config &mconfig, const char *tag, device_t *owner, const XTAL &clock)
: device_t(mconfig, SMS_GRAPHIC, tag, owner, clock)
, device_sms_control_port_interface(mconfig, *this)
, m_buttons(*this, "BUTTONS")
, m_x(*this, "X")
, m_y(*this, "Y")
, m_index(0)
, m_previous_write(0xff)
, m_pressure(0xfd)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void sms_graphic_device::device_start()
{
save_item(NAME(m_index));
save_item(NAME(m_previous_write));
}
//-------------------------------------------------
// sms_peripheral_r - joypad read
//-------------------------------------------------
uint8_t sms_graphic_device::peripheral_r()
{
switch (m_index)
{
case 0: // Initial state / "I am a board"
// If any regular button is pressed raise/lower TL ?
// if ((m_buttons->read() & 0x07) != 0x07)
// return 0xf0;
return 0xd0;
case 1: // Read buttons (active low)
return m_buttons->read();
case 2: // Some thing only FD, FE, and FF cause the other values to be read
return m_pressure >> 4;
case 3:
return m_pressure & 0x0f;
case 4: // High nibble X?
return m_x->read() >> 4;
case 5: // Low nibble X?
return m_x->read() & 0x0f;
case 6: // High nibble Y?
return m_y->read() >> 4;
case 7: // Low Nibble Y?
return m_y->read() & 0x0f;
}
return 0xff;
}
void sms_graphic_device::peripheral_w(uint8_t data)
{
// Check for toggle on TH/TL
if ((data ^ m_previous_write) & 0xc0)
{
m_index++;
}
// If TR is high, restart
if (data & 0x80)
{
m_index = 0;
}
m_previous_write = data;
}
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