Block Copy or Search of memory

Copy or search block of memory

1 Block Copy

2 Block Search of memory

1 - 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.

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

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 BC by one
HL and DE are either incremented (for LDI/LDIR) or decremented (for LDD/LDDR) by one.
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

p/v

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

Opcode Matrix Legend
Instruction Opcode hexSize bytesCycle count		Memory

2 - Block Search of memory

Search block of memory

The Block compare instructions allow for data to be searched for in memory. The programmer needs to configure the following registers to define the properties of the search: HL is the source address to search from; BC is the number of bytes to search. A is set to the value to search for.

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

7	6	5	4	3	2	1	0
1	1	1	0	1	1	0	1	ED
1	0	1	L	D	0	0	1

D 0=Increment, 1=Decrement HL after each iteration.

The CP* instructions compare memory against the Accumulator

Calculate difference between A and content of memory in (HL) to set/clear Z flag
Decrement BC by one
HL is either incremented (for CPI/CPIR) or decremented (for CPD/CPDR) by one.
The CPIR and CPDR instructions will loop back to step one if \( A-(HL) \not = 0 \And BC \not = 0 \)
If the value was found them HL will be set to the byte after or before it depending on the direction being used.

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.

Flags Affected

Flags

p/v

Set if result is negative

Set if A = (HL)

Borrow from bit 4, otherwise 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 Search	CPI EDA1216	CPD EDA9216
Repeat Search	CPIR EDB1221	CPDR EDB9221

Opcode Matrix Legend
Instruction Opcode hexSize bytesCycle count		Memory

Block Copy or Search of memory

Table of Contents

1 - Block Copy

Timing

Flags Affected

Opcode Matrix

2 - Block Search of memory

Timing

Flags Affected

Opcode Matrix