Block Copy

Copy block of memory

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.

$$\begin{rcases} \begin{rcases} HL \longleftarrow HL+1 \\ DE \longleftarrow DE+1 \end{rcases} \text{ if } D = 0\\ \begin{rcases} HL \longleftarrow HL-1 \\DE \longleftarrow DE-1 \end{rcases} \text{ if } D=1 \\BC \longleftarrow BC-1 \end{rcases} \text{repeat while } \begin{cases} L=1\\BC \not = 0 \end{cases}$$

76543210
11101101ED
101LD000

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:

1. Copy a byte of memory from (HL) to (DE)
2. Decrement BC by one
3. HL and DE are either incremented (for LDI/LDIR) or decremented (for LDD/LDDR) by one.
4. The LDIR and LDDR instructions 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 - p/v - -
hReset
p/vNon-repeating: Set if BC-1 != 0, otherwise reset
Repeating: N/A as BC=0 after instruction completes
Opcode Matrix
IncrementDecrement
Single Copy
LDI
EDA0216
LDD
EDA8216
Repeat Copy
LDIR
EDB0221
LDDR
EDB8221
 Instruction Opcode hexSize bytesCycle count Memory

Last modified November 16, 2021: Split Block operations (c052920)