// 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(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; }