The Block copy instructions allow for data to be moved around in memory.
The programmer needs to configure the 16 bit registers to define the properties of the move:
HL is the source address to copy from;
DE is the destination address to copy to;
BC is the number of bytes to copy.
\(\begin{rcases} \begin{rcases} HL \longleftarrow HL+1 \\ DE \longleftarrow DE+1 \end{rcases} \text{ if } D = 0\\ \begin{rcases} HL \longleftarrow HL-1 \\DE \longleftarrow DE-1 \end{rcases} \text{ if } D=1 \\BC \longleftarrow BC-1 \end{rcases} \text{repeat while } \begin{cases} L=1\\BC \not = 0 \end{cases}\)
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | ED |
| 1 | 0 | 1 | L | D | 0 | 0 | 0 |
D 0=Increment, 1=Decrement HL after each iteration.
L If set then if \( BC \not = 0 \) at the end if the instruction then \( PC \longleftarrow PC - 2 \)
so that the instruction is repeated.
If BC=0 at start of a repeatable instruction then 65536 iterations will occur.
The LD* instructions then perform the equivalent of the following:
- Copy a byte of memory from
(HL)to(DE) - Decrement
BCby one HLandDEare either incremented (for LDI/LDIR) or decremented (for LDD/LDDR) by one.- The
LDIRandLDDRinstructions will loop back to step one if \( BC \not = 0 \)
Timing
For the non-repeating instructions, they take 16(4,4,3,5) T-States to execute.
For the repeating instructions, they take either 21(4,4,3,5,5) T-States when they loop and 16(4,4,3,5) T-States when terminating.
Also note, that for these instructions the timing is for each iteration, not for the entire run. So if LDIR is run with BC=4 then the number of T-States for the entire operation would take 79(21+21+21+16) T-States.
Flags Affected
| Flags |
| ||||||||
|---|---|---|---|---|---|---|---|---|---|
| h | Reset | ||||||||
| p/v | Non-repeating: Set if BC-1 != 0, otherwise reset Repeating: N/A as BC=0 after instruction completes |
Opcode Matrix
| Increment | Decrement | |
|---|---|---|
| Single Copy |
LDI
EDA0216 |
LDD
EDA8216 |
| Repeat Copy |
LDIR
EDB0221 |
LDDR
EDB8221 |
|
Instruction
Opcode hexSize bytesCycle count
| Memory |