mirror of
https://github.com/uffejakobsen/acme.git
synced 2024-11-16 23:21:29 +00:00
3db33bafb5
git-svn-id: https://svn.code.sf.net/p/acme-crossass/code-0/trunk@286 4df02467-bbd4-4a76-a152-e7ce94205b78
146 lines
7.0 KiB
Plaintext
146 lines
7.0 KiB
Plaintext
|
|
|
|
ACME
|
|
|
|
...the ACME Crossassembler for Multiple Environments
|
|
|
|
--- Undocumented ("illegal") opcodes ---
|
|
|
|
|
|
In release 0.87, support for some of the undocumented opcodes of the
|
|
NMOS 6502 processor was added.
|
|
In release 0.89, some more were added.
|
|
In release 0.94.8, another one was added (lxa).
|
|
In release 0.95.3, C64DTV2 support was added, which includes these
|
|
opcodes as well.
|
|
In release 0.95.4, the remaining seven were added.
|
|
In release 0.95.6, "ANC" was removed from C64DTV2 mode.
|
|
|
|
Here are the new mnemonics, possible addressing modes and generated
|
|
opcodes (mnemonics in parentheses are used by other sources):
|
|
|
|
| addressing mode |
|
|
mnemonic | 8 8,x 8,y 16 16,x 16,y (8,x) (8),y | performs:
|
|
----------------+--------------------------------------+-----------
|
|
slo (aso) | 07 17 0f 1f 1b 03 13 | asl + ora
|
|
rla (rln) | 27 37 2f 3f 3b 23 33 | rol + and
|
|
sre (lse) | 47 57 4f 5f 5b 43 53 | lsr + eor
|
|
rra (rrd) | 67 77 6f 7f 7b 63 73 | ror + adc
|
|
sax (axs, aax) | 87 97 8f 83 | stx + sta
|
|
lax | a7 b7 af bf a3 b3 | ldx + lda
|
|
dcp (dcm) | c7 d7 cf df db c3 d3 | dec + cmp
|
|
isc (isb, ins) | e7 f7 ef ff fb e3 f3 | inc + sbc
|
|
las (lar, lae) | bb | A,X,S = {addr} & S
|
|
tas (shs, xas) | 9b | S = A & X {addr} = A&X& {H+1}
|
|
sha (axa, ahx) | 9f 93 | {addr} = A & X & {H+1}
|
|
shx (xas, sxa) | 9e | {addr} = X & {H+1}
|
|
shy (say, sya) | 9c | {addr} = Y & {H+1}
|
|
|
|
| addressing mode |
|
|
mnemonic | implied #8 8 8,x 16 16,x | performs:
|
|
----------------+---------------------------------+-----------------------
|
|
anc (ana, anb) | 0b* | A = A & arg, then C=N
|
|
alr/asr | 4b | A = A & arg, then lsr
|
|
arr | 6b | A = A & arg, then ror
|
|
sbx (axs, sax) | cb | X = (A & X) - arg
|
|
dop (nop, skb) | 80** 80 04 14 | skips next byte
|
|
top (nop, skw) | 0c** 0c 1c | skips next two bytes
|
|
nop (skb, skw) | ea 80 04 14 0c 1c | see the two lines above
|
|
jam (kil, hlt) | 02 | crash (wait for reset)
|
|
These two are somewhat unstable, because they involve an arbitrary value:
|
|
ane (xaa, axm) | 8b*** | A = (A | ??) & X & arg
|
|
lxa (lax, atx) | ab*** | A,X = (A | ??) & arg
|
|
|
|
Example:
|
|
!cpu nmos6502 ; activate additional mnemonics...
|
|
lax (some_zp_label,x) ; ...and use them. No, this
|
|
dcp (other_zp_label),y ; example does not make sense.
|
|
|
|
*) Up until ACME version 0.95.1, anc#8 generated opcode 0x2b. Since
|
|
ACME version 0.95.2, anc#8 generates opcode 0x0b. Both opcodes work
|
|
the same way on a real NMOS 6502 CPU, but they do not work on the
|
|
C64DTV2.
|
|
Using the "--dialect" CLI switch does not change the generated opcode!
|
|
|
|
**) Note that DOP ("double nop") and TOP ("triple nop") can be used
|
|
with implied addressing, but the generated opcodes are those for
|
|
immediate and 16-bit absolute addressing, respectively, This way DOP
|
|
and TOP can be used to skip the following one- or two-byte
|
|
instruction.
|
|
Using DOP/TOP with x-indexed addressing might have its uses when
|
|
timing is critical (crossing a page border adds a penalty cycle).
|
|
Unless using implied addressing, DOP/TOP can also be written as NOP.
|
|
|
|
***) ANE and LXA first perform an ORA with an arbitrary(!) value and
|
|
then perform an AND with the given argument. So they are unstable and
|
|
therefore useless - unless the given argument is zero:
|
|
ANE #0 reliably clears A - which is still useless; just use LDA #0.
|
|
LXA #0 reliably clears both A and X.
|
|
ACME will output a warning if these opcodes get assembled with a
|
|
nonzero argument.
|
|
|
|
There is no guarantee that these opcodes actually work on a given 6502
|
|
(or 6510, or 8500, or 8501, or 8502) CPU. But as far as I know, nobody
|
|
ever found an unmodified C64/C128 where these illegals didn't work.
|
|
|
|
These illegals will definitely *not* work on 65c02 and 65816 CPUs. But
|
|
I really should not have to tell you that ;)
|
|
|
|
Because there are no official mnemonics for these opcodes, different
|
|
people use different names for them. I hope my choices are not too
|
|
exotic for your taste.
|
|
|
|
Just for the sake of completeness: Here are all the remaining opcodes
|
|
(the ones ACME won't generate even with "nmos6502" cpu chosen):
|
|
|
|
Opcode| Description C64DTV2
|
|
------+--------------------------------------------------------------
|
|
12 | same as 02 and others jam CRASH bra rel
|
|
1a | same as (*legal*) ea nop
|
|
22 | same as 02 and others jam CRASH
|
|
2b | same as 0b anc #8 dop
|
|
32 | same as 02 and others jam CRASH sac #8
|
|
34 | same as 14 and others dop 8,x
|
|
3a | same as (*legal*) ea nop
|
|
3c | same as 1c and others top 16,x
|
|
42 | same as 02 and others jam CRASH sir #8
|
|
44 | same as 04 dop 8
|
|
52 | same as 02 and others jam CRASH
|
|
54 | same as 14 and others dop 8,x
|
|
5a | same as (*legal*) ea nop
|
|
5c | same as 1c and others top 16,x
|
|
62 | same as 02 and others jam CRASH
|
|
64 | same as 04 dop 8
|
|
72 | same as 02 and others jam CRASH
|
|
74 | same as 14 and others dop 8,x
|
|
7a | same as (*legal*) ea nop
|
|
7c | same as 1c and others top 16,x
|
|
82 | same as c2/e2 dop #8, but said to CRASH sometimes
|
|
89 | same as 80 dop #8
|
|
92 | same as 02 and others jam CRASH
|
|
b2 | same as 02 and others jam CRASH
|
|
c2 | same as 82/e2 dop #8, but said to CRASH sometimes
|
|
d2 | same as 02 and others jam CRASH
|
|
d4 | same as 14 and others dop 8,x
|
|
da | same as (*legal*) ea nop
|
|
dc | same as 1c and others top 16,x
|
|
e2 | same as 82/c2 dop #8, but said to CRASH sometimes
|
|
eb | same as (*legal*) e9 sbc #8
|
|
f2 | same as 02 and others jam CRASH
|
|
f4 | same as 14 and others dop 8,x
|
|
fa | same as (*legal*) ea nop
|
|
fc | same as 1c and others top 16,x
|
|
|
|
For more information about what these opcodes do, see these documents:
|
|
John West, Marko Mäkelä. '64doc' file, 1994/06/03.
|
|
Extra Instructions Of The 65XX Series CPU, Adam Vardy, 27 Sept. 1996
|
|
6502 Undocumented Opcodes, by Freddy Offenga, 5/17/1997
|
|
AAY64 (All About Your 64)
|
|
|
|
...but the most comprehensive work is:
|
|
|
|
"No More Secrets - NMOS 6510 Unintended Opcodes"
|
|
|
|
Download it from https://csdb.dk/release/?id=185341
|
|
or ask google for the latest version.
|