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// license:BSD-3-Clause
// copyright-holders:Ryan Holtz
/*
First-gen DEC PDP-8 disassembler
Written by MooglyGuy
*/
#include "emu.h"
static char *output;
offs_t pdp8_dasm_one(char *buffer, offs_t pc, UINT16 op)
{
UINT8 opcode = (op >> 011) & 07;
UINT16 current_page = pc & 07600;
UINT16 zero_addr = op & 0177;
UINT16 current_addr = current_page | zero_addr;
bool indirect = (op & 0400) ? true : false;
bool zero_page = (op & 0200) ? false : true;
output = buffer;
switch (opcode)
{
case 0:
output += sprintf(buffer, "AND %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 1:
output += sprintf(buffer, "TAD %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 2:
output += sprintf(buffer, "ISZ %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 3:
output += sprintf(buffer, "DCA %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 4:
output += sprintf(buffer, "JMS %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 5:
output += sprintf(buffer, "JMP %c %05o", indirect ? 'I' : ' ', zero_page ? zero_addr : current_addr);
break;
case 6:
output += sprintf(buffer, "IOT %03o %01o", (op >> 03) & 077, op & 07);
break;
case 7:
{
bool group2 = ((op & 0401) == 0400);
if (!group2)
{
if (!(op & 0377))
{
output += sprintf(buffer, "NOP ");
}
else
{
if (op & 0200)
{
output += sprintf(buffer, "CLA ");
}
if (op & 0100)
{
output += sprintf(buffer, "CLL ");
}
if (op & 040)
{
output += sprintf(buffer, "CMA ");
}
if (op & 020)
{
output += sprintf(buffer, "CML ");
}
if (op & 01)
{
output += sprintf(buffer, "IAC ");
}
if (op & 010)
{
if (op & 02)
{
output += sprintf(buffer, "RTR ");
}
else
{
output += sprintf(buffer, "RAR ");
}
}
if (op & 04)
{
if (op & 02)
{
output += sprintf(buffer, "RTL ");
}
else
{
output += sprintf(buffer, "RAL ");
}
}
}
}
else
{
if (!(op & 0377))
{
output += sprintf(buffer, "NOP ");
}
else
{
if (op & 010)
{
if (!(op & 0160))
{
output += sprintf(buffer, "SKP ");
}
else
{
if (op & 0100)
{
output += sprintf(buffer, "SPA ");
}
if (op & 040)
{
output += sprintf(buffer, "SNA ");
}
if (op & 020)
{
output += sprintf(buffer, "SZL ");
}
}
}
else
{
if (op & 0100)
{
output += sprintf(buffer, "SMA ");
}
if (op & 040)
{
output += sprintf(buffer, "SZA ");
}
if (op & 020)
{
output += sprintf(buffer, "SNL ");
}
}
if (op & 0200)
{
output += sprintf(buffer, "CLA ");
}
if (op & 04)
{
output += sprintf(buffer, "OSR ");
}
if (op & 02)
{
output += sprintf(buffer, "HLT ");
}
}
}
}
}
return 2 | DASMFLAG_SUPPORTED;
}
/*****************************************************************************/
CPU_DISASSEMBLE( pdp8 )
{
UINT16 op = (*(UINT8 *)(opram + 0) << 8) |
(*(UINT8 *)(opram + 1) << 0);
return pdp8_dasm_one(buffer, pc, op);
}
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