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comparison README.txt @ 184:ef64e3f4e229 current

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merge
author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Sat, 30 Jul 2022 18:22:06 +0900
parents 2088fd998865
children
comparison
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183:0eb94a8e4d0d 184:ef64e3f4e229
168 +--------------- $80 168 +--------------- $80
169 169
170 170
171 # differences from real 6809: 171 # differences from real 6809:
172 172
173 ldd #$0fc9 173 ldd #$0fc9
174 addb #$40 174 addb #$40 ; $C9+$40 -> $09 -> C=1
175 adca #$00 175 adca #$00 ; $0F+C -> $10 -> H=1
176 176
177 H is set on VCC but not on real 6809, sim6809 does what? 177 Should Set the half-carry!
178
179 For this example the half-carry is set on a real 6809, also correctly
180 emulated on the VCC. v09s does the same.
181
182 According to "Motorola 6809 and Hitachi 6309 Programmer's Reference"
183 the half-carry is only properly set for ADD and ADC (on 8-bit accumulators).
184 For ASR, ASL (= LSL), CMP, SBC, SUB this condition flag is undefined.
185 The v09s simulator calculates the half-carry also for ASR and ASL.
186
187 ASL does the following:
188 * sets H if bit 4 was set.
189 * clears H if bit was not set.
190
191 ASR (=LSR) does the following:
192 * xxx1 xxxx --- (LSR|ASR) ---> xxxx 1xxx => H=1
193 * xxx0 xxxx --- (LSR|ASR) ---> xxxx 0xxx => H=0
194
195
196 But note: LSR never touches the half-carry!
197
198
199 ## TFR/EXG with unaligned register sizes
200
201 See http://archive.worldofdragon.org/phpBB3/viewtopic.php?f=8&t=5512
202 Points to the 6309 behavior which is not compatible to 6809!
203
204 tfr x,b ; 6809,6309: b low byte of x, a unchanged
205 tfr x,a ; 6809, a low byte of x, b unchanged
206 ; on a 6309: a high(!) byte of x, b unchanged
207
208 Might be used to get the low byte out of an index register without harm
209 the A register:
210
211 instead of
212 pushs a
213 tfr x,d
214 andb #$1f
215 it could be used
216 tfr x,b
217 andb #$1f ; a left untouched!
218
219 REF: http://www.6809.org.uk/dragon/illegal-opcodes.shtml
220 REF: http://archive.worldofdragon.org/phpBB3/viewtopic.php?f=8&t=4886
221
222 tfr a,x ; low byte of x has value of a, high byte is $FF
223 tfr b,x ; low byte of x has value of b, high byte is $FF
224
225 exg a,x ; low byte of x has value of a, high byte is $FF
226 exg b,x ; low byte of x has value of b, high byte is $FF
227
228 According to Motorola 6809 and Hitachi 6309 Programmer's Reference
229
230 Except for the case where the first operand is 8 bit and register CC or DP:
231 In this case the 16-bit register has the value of the 8-bit register in
232 high and low byte!
178 233
179 234
180 ### special behavior 235 ### special behavior
181 236
182 swi2 output character (STDOUT) in register B 237 swi2 output character (STDOUT) in register B