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// license:BSD-3-Clause
// copyright-holders:Nigel Barnes
/**********************************************************************
Memex B20 20K RAM expansion
This is a DIY project from the May 1984 issue of Electronics and
Computing, with part two of the project in the August 1984 issue.
**********************************************************************/
#include "emu.h"
#include "memex.h"
//**************************************************************************
// DEVICE DEFINITIONS
//**************************************************************************
DEFINE_DEVICE_TYPE(BBC_MEMEXB20, bbc_memexb20_device, "bbc_memexb20", "Memex-B20 RAM expansion");
//-------------------------------------------------
// ROM( memexb20 )
//-------------------------------------------------
ROM_START(memexb20)
ROM_REGION(0x2000, "exp_rom", 0)
ROM_LOAD("memex-b20_v2.2.rom", 0x0000, 0x2000, CRC(98ee8eb6) SHA1(aad311797e204b0b69450460f8b4605409c31ddd))
ROM_END
//-------------------------------------------------
// rom_region - device-specific ROM region
//-------------------------------------------------
const tiny_rom_entry *bbc_memexb20_device::device_rom_region() const
{
return ROM_NAME(memexb20);
}
//**************************************************************************
// LIVE DEVICE
//**************************************************************************
//-------------------------------------------------
// bbc_memexb20_device - constructor
//-------------------------------------------------
bbc_memexb20_device::bbc_memexb20_device(const machine_config &mconfig, const char *tag, device_t *owner, const XTAL &clock)
: device_t(mconfig, BBC_MEMEXB20, tag, owner, clock)
, device_bbc_internal_interface(mconfig, *this)
, m_shadow(false)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void bbc_memexb20_device::device_start()
{
address_space &program = m_maincpu->space(AS_PROGRAM);
program.install_write_handler(0xd000, 0xd000, write8smo_delegate(*this, FUNC(bbc_memexb20_device::enable_w)));
program.install_write_handler(0xc000, 0xc000, write8smo_delegate(*this, FUNC(bbc_memexb20_device::disable_w)));
m_ram = make_unique_clear<uint8_t[]>(0x5000);
/* register for save states */
save_item(NAME(m_shadow));
save_pointer(NAME(m_ram), 0x5000);
}
//**************************************************************************
// IMPLEMENTATION
//**************************************************************************
void bbc_memexb20_device::enable_w(uint8_t data)
{
m_shadow = true;
}
void bbc_memexb20_device::disable_w(uint8_t data)
{
m_shadow = false;
}
uint8_t bbc_memexb20_device::ram_r(offs_t offset)
{
uint8_t data = 0xff;
if (m_shadow && offset >= 0x3000)
data = m_ram[offset - 0x3000];
else
data = m_mb_ram->pointer()[offset];
return data;
}
void bbc_memexb20_device::ram_w(offs_t offset, uint8_t data)
{
if (m_shadow && offset >= 0x3000)
m_ram[offset - 0x3000] = data;
else
m_mb_ram->pointer()[offset] = data;
}
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