LDP HL,(HL)
LDP HL,(IX)
LDP HL,(IY)     Load Physical     Rabbit 2000/3000/4000 Instruction

Opcode	Instruction	Clocks	Operation
ED 6C	LDP HL,(HL)	10 (2,2,2,2,2)	L = (HL) H = (HL + 1) (Addr[19:16] = A[3:0])
DD 6C	LDP HL,(IX)	10 (2,2,2,2,2)	L = (IX) H = (IX + 1) (Addr[19:16] = A[3:0])
FD 6C	LDP HL,(IY)	10 (2,2,2,2,2)	L = (IY) H = (IY + 1) (Addr[19:16] = A[3:0])

Flags				ALTD			IOI/IOE
S	Z	L/V	C	F	R	SP	S	D
-	-	-	-

Description

These instructions are used to access 20-bit addresses. In all cases, the four most significant bits of the 20- bit address (bits 19 through 16) are defined as the four least significant bits of A (bits 3 though 0). The LDP instructions bypass the MMU's address translation unit for direct access to the 20-bit memory address space.

• LDP HL,(HL): Loads L with the data whose 16 least significant bits of its 20-bit address are the data in HL, and then loads H with the data in the following 20-bit address.

• LDP HL,(IX): Loads L with the data whose 16 least significant bits of its 20-bit address are the data in IX, and then loads H with the data in the following 20-bit address.

• LDP HL,(IY): Loads L with the data whose 16 least significant bits of its 20-bit address are the data in IY, and then loads H with the data in the following 20-bit address.

Note that the LDP instructions wrap around on a 64K page boundary. Since the LDP instruction operates on two-byte values, the second byte will wrap around and be written at the start of the page if you try to read or write across a page boundary. Thus, if you fetch or store at address 0xn,0xFFFF, you will get the bytes located at 0xn, 0xFFFF and 0xn,0x0000 instead of 0xn,0xFFFF and 0x(n+1),0x0000 as you might expect. Therefore, do not use LDP at any physical address ending in 0xFFFF.