jcs.org
fork of PCE focusing on macplus, supporting DaynaPort SCSI network emulation
1/*****************************************************************************
2 * pce *
3 *****************************************************************************/
4
5/*****************************************************************************
6 * File name: src/cpu/e6502/ea.c *
7 * Created: 2004-05-25 by Hampa Hug <hampa@hampa.ch> *
8 * Copyright: (C) 2004-2010 Hampa Hug <hampa@hampa.ch> *
9 *****************************************************************************/
10
11/*****************************************************************************
12 * This program is free software. You can redistribute it and / or modify it *
13 * under the terms of the GNU General Public License version 2 as published *
14 * by the Free Software Foundation. *
15 * *
16 * This program is distributed in the hope that it will be useful, but *
17 * WITHOUT ANY WARRANTY, without even the implied warranty of *
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General *
19 * Public License for more details. *
20 *****************************************************************************/
21
22
23#include "e6502.h"
24#include "internal.h"
25
26#include <stdlib.h>
27#include <stdio.h>
28#include <stdarg.h>
29
30
31unsigned char e6502_get_imm (e6502_t *c)
32{
33 e6502_get_inst1 (c);
34
35 c->ea_page = 0;
36
37 return (c->inst[1]);
38}
39
40unsigned short e6502_get_ea_idx_ind_x (e6502_t *c)
41{
42 unsigned ial, adl, adh;
43
44 e6502_get_inst1 (c);
45
46 ial = c->inst[1];
47 ial = (ial + e6502_get_x (c)) & 0xff;
48
49 adl = e6502_get_mem8 (c, ial);
50 adh = e6502_get_mem8 (c, (ial + 1) & 0xff);
51
52 c->ea = (adh << 8) | adl;
53 c->ea_page = 0;
54
55 return (c->ea);
56}
57
58unsigned short e6502_get_ea_zpg (e6502_t *c)
59{
60 e6502_get_inst1 (c);
61
62 c->ea = c->inst[1];
63 c->ea_page = 0;
64
65 return (c->ea);
66}
67
68unsigned short e6502_get_ea_abs (e6502_t *c)
69{
70 e6502_get_inst2 (c);
71
72 c->ea = ((unsigned short) c->inst[2] << 8) + c->inst[1];
73 c->ea_page = 0;
74
75 return (c->ea);
76}
77
78unsigned short e6502_get_ea_ind_idx_y (e6502_t *c)
79{
80 unsigned ial, adl, adh;
81
82 e6502_get_inst1 (c);
83
84 ial = c->inst[1];
85
86 adl = e6502_get_mem8 (c, ial);
87 adh = e6502_get_mem8 (c, (ial + 1) & 0xff);
88
89 adl += e6502_get_y (c);
90
91 if (adl < 0x100) {
92 c->ea_page = 0;
93 }
94 else {
95 c->ea_page = 1;
96 adl = adl & 0xff;
97 adh = (adh + 1) & 0xff;
98 }
99
100 c->ea = (adh << 8) | adl;
101
102 return (c->ea);
103}
104
105unsigned short e6502_get_ea_zpg_x (e6502_t *c)
106{
107 e6502_get_inst1 (c);
108
109 c->ea = (c->inst[1] + e6502_get_x (c)) & 0xff;
110 c->ea_page = 0;
111
112 return (c->ea);
113}
114
115unsigned short e6502_get_ea_zpg_y (e6502_t *c)
116{
117 e6502_get_inst1 (c);
118
119 c->ea = (c->inst[1] + e6502_get_y (c)) & 0xff;
120 c->ea_page = 0;
121
122 return (c->ea);
123}
124
125unsigned short e6502_get_ea_abs_y (e6502_t *c)
126{
127 unsigned short tmp;
128
129 e6502_get_inst2 (c);
130
131 tmp = e6502_mk_uint16 (c->inst[1], c->inst[2]);
132 c->ea = (tmp + e6502_get_y (c)) & 0xffff;
133
134 if ((tmp ^ c->ea) & 0xff00) {
135 c->ea_page = 1;
136 }
137 else {
138 c->ea_page = 0;
139 }
140
141 return (c->ea);
142}
143
144unsigned short e6502_get_ea_abs_x (e6502_t *c)
145{
146 unsigned short tmp;
147
148 e6502_get_inst2 (c);
149
150 tmp = e6502_mk_uint16 (c->inst[1], c->inst[2]);
151 c->ea = (tmp + e6502_get_x (c)) & 0xffff;
152
153 if ((tmp ^ c->ea) & 0xff00) {
154 c->ea_page = 1;
155 }
156 else {
157 c->ea_page = 0;
158 }
159
160 return (c->ea);
161}