User’s Manual
39
3.3.8 Input/Output Instructions
The Rabbit uses an entirely different scheme for accessing input/output devices. Any
memory access instruction may be prefixed by one of two prefixes, one for internal I/O
space and one for external I/O space. When so prefixed, the memory instruction is turned
into an I/O instruction that accesses that I/O space at the I/O address specified by the 16-
bit memory address used. For example
IOI LD A,(0x85) ; loads A register with contents
; of internal I/O register at location 0x85.
LD IY,0x4000
IOE LD HL,(IY+5) ; get word from external I/O location 0x4005
By using the prefix approach, all the 16-bit memory access instructions are available for
reading and writing I/O locations. The memory mapping is bypassed when I/O operations
are executed.
I/O writes to the internal I/O registers require only two clocks, rather than the minimum of
three clocks required for writes to memory or external I/O devices.
Summary of Contents for Rabbit 2000
Page 2: ...Rabbit 3000 Microprocessor User s Manual 019 0108 040731 O ...
Page 9: ...Rabbit 3000 Microprocessor ...
Page 29: ...20 Rabbit 3000 Microprocessor ...
Page 64: ...User s Manual 55 5 PIN ASSIGNMENTS AND FUNCTIONS ...
Page 79: ...70 Rabbit 3000 Microprocessor ...
Page 80: ...User s Manual 71 6 RABBIT INTERNAL I O REGISTERS ...
Page 123: ...114 Rabbit 3000 Microprocessor ...
Page 137: ...128 Rabbit 3000 Microprocessor ...
Page 157: ...148 Rabbit 3000 Microprocessor ...
Page 207: ...198 Rabbit 3000 Microprocessor ...
Page 249: ...240 Rabbit 3000 Microprocessor ...
Page 255: ...246 Rabbit 3000 Microprocessor ...
Page 277: ...268 Rabbit 3000 Microprocessor ...
Page 343: ...334 Rabbit 3000 Microprocessor ...
Page 345: ......