19
2.1.3
System Registers
System registers consist of four 32-bit registers: multiply and accumulate registers high and low
(MACH and MACL), procedure register (PR), and program counter (PC). The multiply and
accumulate registers store the results of multiply and accumulate operations. The procedure
register stores the return address for a subroutine procedure. The program counter stores program
addresses to control the flow of the processing.
MACL
PR
PC
(Sign extended)
MACH
31
9
0
0
0
31
31
Multiply and accumulate (MAC) registers
high and low (MACH, MACL): Store the
results of multiply and accumulate opera-
tions. MACH is sign-extended when read
because only the lowest 10 bits are valid.
Procedure register (PR): Stores the return
address for a subroutine procedure.
Program counter (PC): Indicates the
fourth byte (second instruction) after
the current instruction.
Figure 2.3 System Registers
2.1.4
Initial Values of Registers
Table 2.1 lists the values of the registers after reset.
Table 2.1
Initial Values of Registers
Classification
Register
Initial Value
General registers
R0–R14
Undefined
R15 (SP)
Value of the stack pointer in the vector address table
Control registers
SR
Bits I3–I0 are 1111(H'F), reserved bits are 0, and other
bits are undefined
GBR
Undefined
VBR
H'00000000
System registers
MACH, MACL, PR
Undefined
PC
Value of the program counter in the vector address table
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