does those opcodes exists?

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By PingPong

Prophet (4093)

PingPong's picture

12-09-2009, 12:32

rl ixl ?
srl iyl ?

i suppose no... Tongue

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By PingPong

Prophet (4093)

PingPong's picture

12-09-2009, 20:55

I also suppose no one know.... Cool

By hap

Paragon (2042)

hap's picture

12-09-2009, 21:15

they don't exist

By Leo

Paragon (1236)

Leo's picture

12-09-2009, 21:22

if rl l or srl l exist why would not these undocumented opcode exist ?
like DD CB 3D ??

By hap

Paragon (2042)

hap's picture

12-09-2009, 21:49

Because dd/fd+cb stuff results in:
opcode (x + displacement),reg

By Vampier

Prophet (2409)

Vampier's picture

13-09-2009, 09:44

what is an opcode?

By PingPong

Prophet (4093)

PingPong's picture

13-09-2009, 11:01

what is an opcode?
the numerical (often in hexadecimal) representation of an assembly instruction, without operands.
For example the LD A,10 on z80 has opcode $3E
the other byte, 10 (dec) is the operand.

By Metalbrain

Expert (67)

Metalbrain's picture

14-09-2009, 13:04

Because dd/fd+cb stuff results in:

opcode (x + displacement),reg

It depends on the instructions.

for those starting with 00:

opcode (hl) results in: opcode (x + displacement)

opcode reg results in: ld reg, opcode (x + displacement)

(so we'd get "ld l, rl (ix+dd)" instead of "rl ixl")

those starting with 01 (bit):
bit n,whatever > bit n,(x + displacement)

those starting with 10 or 11 (res and set):

opcode n,(hl) results in: opcode n,(x + displacement)

opcode n,reg results in: ld reg, opcode n,(x + displacement)

By Eugeny_Brychkov

Paragon (1232)

Eugeny_Brychkov's picture

12-10-2009, 23:02

RL (IX+00) = DD CB 00 16
SRL (IY+00) = FD CB 00 3E

Look into the source; ixl and iyl may be defined as macros.

By Yukio

Paragon (1540)

Yukio's picture

13-10-2009, 06:08

what is an opcode?
I think that it is something like "OperationCode" (Machine Code) for the microprocessor ... There are some spaces on the 255 combinations (8-bit) that the Z80 microprocessor use.

It could be Hexadecimal ,Binary, Decimal or even others. Into the Z80 Manual there are several opcodes listed.
You can download the manual here. It is *FREE*.

By [D-Tail]

Ascended (8263)

[D-Tail]'s picture

16-10-2009, 10:21

Yukio: hexadecimal/binary/decimal radices are just methods to represent real numbers. A convention is that opcodes are always represented in hexadecimal when listed with mnemonics (the textual representation of the opcode, like LD A,<x> ) or in binary when specified in an instruction set specification: this allows for generalities in the opcodes to be identified easily, which in turn identifies similarities in the configuration of a processor's data path.

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