
66
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 the Accumulator (bits 3 though 0).
The LDP instructions bypass the MMU’s address translation unit for direct access to the 20-bit memory
address space. These instructions are implemented for the Rabbit and are not available for the Z180.
•
LDP HL,(mn):
Loads the register L with the data whose 16 least significant bits of its 20-bit
address are the 16-bit constant mn, and then loads the register H with the data in the following
20-bit address.
•
LDP IX,(mn):
Loads the low order byte of index register 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 index register 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
-
-
-
-
Содержание 2000
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