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author | 2022-05-15 16:15:00 +0100 | |
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committer | 2022-05-15 16:15:00 +0100 | |
commit | 3377ee1d7985fe6a2b4d79dd5d75c828bccbbbc2 (patch) | |
tree | 2b11cf96911a5ea38ae073f398d5fcdecc4dbaf6 /src/devices/bus/bbc/internal/memex.cpp | |
parent | 74728bc4d42ba21de9a58ad0442a413575e7e357 (diff) |
bus/bbc/internal: Added the Memex-B20 board.
Diffstat (limited to 'src/devices/bus/bbc/internal/memex.cpp')
-rw-r--r-- | src/devices/bus/bbc/internal/memex.cpp | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/src/devices/bus/bbc/internal/memex.cpp b/src/devices/bus/bbc/internal/memex.cpp new file mode 100644 index 00000000000..809313e4c68 --- /dev/null +++ b/src/devices/bus/bbc/internal/memex.cpp @@ -0,0 +1,109 @@ +// 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, uint32_t 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; +} |