Rabbit 2000 Instruction & Reference Manual

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Rabbit 2000 Instruction & Reference Manual Manual pdf 93 page image

Instruction Reference Manual 89DescriptionThese instructions are used to access 20-bit addresses. In all cases, the four most significant bits of the 20-bitaddress (bits 19 through 16) are defined as the four least significant bits of A (bits 3 though 0). The LDPinstructions bypass the MMU’s address translation unit for direct access to the 20-bit memory address space.• LDP (HL),HL: Loads the memory location whose 16 least significant bits of its 20-bitaddress are the data in HL with the data in L, and then loads the following 20-bit address with thedata in H.• LDP (IX),HL: Loads the memory location whose 16 least significant bits of its 20-bitaddress are the data in IX with the data in L, and then loads the following 20-bit address with thedata in H.• LDP (IY),HL: Loads the memory location whose 16 least significant bits of its 20-bitaddress are the data in IY with the data in L, and then loads the following 20-bit address with thedata in H.Note that the LDP instructions wrap around on a 64K page boundary. Since the LDP instruction operates ontwo-byte values, the second byte will wrap around and be written at the start of the page if you try to read orwrite across a page boundary. Thus, if you fetch or store at address 0xn,0xFFFF, you will get the byteslocated 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.LDP (HL),HLLDP (IX),HLLDP (IY),HLOpcode Instruction Clocks OperationED 64 LDP (HL),HL 12 (2,2,2,3,3) (HL) = L; (HL + 1) = H.(Addr[19:16] = A[3:0])DD 64 LDP (IX),HL 12 (2,2,2,3,3) (IX) = L; (IX + 1) = H.(Addr[19:16] = A[3:0])FD 64 LDP (IY),HL 12 (2,2,2,3,3) (IY) = L; (IY + 1) = H.(Addr[19:16] = A[3:0])Flags ALTD I/OS Z L/V C F R SP S D- - - -