Rabbit 3000 User Manual - 3.  D

User’s Manual

21

3.  D

ETAILS

ON

 R

ABBIT

M

ICROPROCESSOR

 F

EATURES

3.1  Processor Registers

The Rabbit’s registers are nearly identical to those of the Z180 or the Z80. The figure 

below shows the register layout. The XPC and IP registers are new. The EIR register is the 

same as the Z80 I register, and is used to point to a table of interrupt vectors for the exter-

nally generated interrupts. The IIR register occupies the same logical position in the 

instruction set as the Z80 R register, but its function is to point to an interrupt vector table 

for internally generated interrupts.

Figure 3-1.  Rabbit Registers

A

F

H

L

D

E

B

C

IX

IY

SP

PC

A’

F ’

H ’

L’

D ’

E ’

B ’

C ’

Alternate Registers

IP

XPC

IIR

EIR

F - flag register layout

S

Z

V

C

S-sign, Z-zero, V-overflow, C-carry

x

x

x

x

Bits marked "x" are read/write.

8 / 16 bit

registers

A- 8-bit accumulator

F - flags register

HL- 16-bit accumulator

IX, IY - Index registers/alt accum’s

SP - stack pointer

PC- program counter

XPC - extension of program counter

IIR - internal interrupt register

EIR-external interrupt register

IP - interrupt priority register