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-rw-r--r--src/devices/machine/tmc0999.cpp97
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diff --git a/src/devices/machine/tmc0999.cpp b/src/devices/machine/tmc0999.cpp
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+// license:BSD-3-Clause
+// copyright-holders:hap
+/*
+
+Texas Instruments TMC0999 256x4 RAM
+
+It's not a standard RAM chip, it has separate pins for input and output
+and an internal address latch.
+
+TODO:
+- no official documentation is known to exist, unknown if anything is missing
+- pin names are unknown
+
+*/
+
+#include "emu.h"
+#include "tmc0999.h"
+
+
+DEFINE_DEVICE_TYPE(TMC0999, tmc0999_device, "tmc0999", "TI TMC0999 RAM")
+
+//-------------------------------------------------
+// constructor
+//-------------------------------------------------
+
+tmc0999_device::tmc0999_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock) :
+ device_t(mconfig, TMC0999, tag, owner, clock)
+{ }
+
+
+//-------------------------------------------------
+// device_start - device-specific startup
+//-------------------------------------------------
+
+void tmc0999_device::device_start()
+{
+ // zerofill
+ m_data = 0;
+ m_wr = 0;
+ m_rd = 0;
+ m_adr_strobe = 0;
+ m_ram_address = 0;
+ memset(m_ram, 0, sizeof(m_ram));
+
+ // register for savestates
+ save_item(NAME(m_data));
+ save_item(NAME(m_wr));
+ save_item(NAME(m_rd));
+ save_item(NAME(m_adr_strobe));
+ save_item(NAME(m_ram_address));
+ save_item(NAME(m_ram));
+}
+
+
+//-------------------------------------------------
+// handlers
+//-------------------------------------------------
+
+void tmc0999_device::di_w(u8 data)
+{
+ m_data = data & 0xf;
+}
+
+u8 tmc0999_device::do_r()
+{
+ u8 data = m_rd ? m_ram[m_ram_address] : 0;
+ return data & 0xf;
+}
+
+void tmc0999_device::wr_w(int state)
+{
+ state = state ? 1 : 0;
+
+ // write to RAM on rising edge
+ if (state && !m_wr)
+ m_ram[m_ram_address] = m_data;
+ m_wr = state;
+}
+
+void tmc0999_device::rd_w(int state)
+{
+ // enable data outputs
+ m_rd = state ? 1 : 0;
+}
+
+void tmc0999_device::adr_w(int state)
+{
+ state = state ? 1 : 0;
+
+ // set RAM address lo on rising edge
+ // set RAM address hi on falling edge
+ if (state && !m_adr_strobe)
+ m_ram_address = (m_ram_address & 0xf0) | m_data;
+ else if (!state && m_adr_strobe)
+ m_ram_address = (m_ram_address & 0x0f) | m_data << 4;
+ m_adr_strobe = state;
+}