
R01UH0040EJ0100 Rev.1.00
Page 120 of 1657
Sep 8, 2011
RX630 Group
2. CPU
2.2.3
Register Associated with DSP Instructions
2.2.3.1
Accumulator (ACC)
The accumulator (ACC) is a 64-bit register used for DSP instructions. The accumulator is also used for the multiply and
multiply-and-accumulate instructions; EMUL, EMULU, FMUL, MUL, and RMPA, in which case the prior value in the
accumulator is modified by execution of the instruction.
Use the MVTACHI and MVTACLO instructions for writing to the accumulator. The MVTACHI and MVTACLO
instructions write data to the higher-order 32 bits (bits 63 to 32) and the lower-order 32 bits (bits 31 to 0), respectively.
Use the MVFACHI and MVFACMI instructions for reading data from the accumulator. The MVFACHI and MVFACMI
instructions read data from the higher-order 32 bits (bits 63 to 32) and the middle 32 bits (bits 47 to 16), respectively.
2.3
Processor Mode
The RX CPU supports two processor modes, supervisor and user. These processor modes enable the realization of a
hierarchical CPU resource protection.
Each processor mode imposes a level on rights of access to the CPU resources and the instructions that can be executed.
Supervisor mode carries greater rights than those of user mode.
The initial state after a reset is supervisor mode.
2.3.1
Supervisor Mode
In supervisor mode, all CPU resources are accessible and all instructions are available. However, writing to the processor
mode select bit (PM) in the processor status word (PSW) by executing an MVTC or a POPC instruction will be ignored.
2.3.2
User Mode
In user mode, write access to the CPU resources listed below is restricted. The restriction applies to any instruction
capable of write access.
Some bits (bits IPL[3:0], PM, U, and I) in the processor status word (PSW)
Interrupt stack pointer (ISP)
Interrupt table register (INTB)
Backup PSW (BPSW)
Backup PC (BPC)
Fast interrupt vector register (FINTV)
2.3.3
Privileged Instruction
Privileged instructions can only be executed in supervisor mode. Executing a privileged instruction in user mode
produces a privileged instruction exception. Privileged instructions include the RTFI, MVTIPL, RTE, and WAIT
instructions.
Range for reading by MVFACMI
b63
b48 b47
b32
b31
b16 b15
b0
Range for reading and writing by
MVTACHI and MVFACHI
Range for writing by MVTACLO
Value after reset:
Undefined