Rabbit 2000, Instruction & Reference Manual

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92 Rabbit 2000/3000 Microprocessor
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,(mn):
Loads L with the data whose 16 least significant bits of its 20-bit address are
the 16-bit constant mn, and then loads H with the data in the following 20-bit address.
•
LDP IX,(mn):
Loads the low order byte of IX with the data whose 16 least significant bits
of its 20-bit address are the 16-bit constant mn, and then loads the high order byte of IX with the
data in the following 20-bit address.
•
LDP IY,(mn):
Loads the low order byte of IY with the data whose 16 least significant bits
of its 20-bit address are the 16-bit constant mn, and then loads the high order byte of IY 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.
LDP HL,( mn )
LDP IX,( mn )
LDP IY,( mn )
Opcode Instruction Clocks Operation
ED 6D n m LDP HL,( mn ) 13* L = ( mn ); H = ( mn + 1).
(Addr[19:16] = A[3:0])
DD 6D n m LDP IX,( mn ) 13* IX
(low)
= ( mn ); IX
(high)
= ( mn + 1).
(Addr[19:16] = A[3:0])
FD 6D n m LDP IY,( mn ) 13* IY
(low)
= ( mn ); IY
(high)
= ( mn + 1).
(Addr[19:16] = A[3:0])
*Clocking: 13 (2,2,2,2,1,2,2)
Flags ALTD I/O
S Z L/V C F R SP S D
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