CPU
2.3 Control Registers
2
2.3.2 Condition Bit Register: CBR (CR1)
The Condition Bit Register (CBR) is derived from the PSW register by extracting its Condition (C) bit. The value
written to the PSW register’s C bit is reflected in this register. The register can only be read. (Writing to the
register with the MVTC instruction is ignored.)
After reset, the value of CBR is H’0000 0000.
b0
0
b31
C
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CBR
2.3.3 Interrupt Stack Pointer: SPI (CR2) and User Stack Pointer: SPU (CR3)
The Interrupt Stack Pointer (SPI) and the User Stack Pointer (SPU) retain the address of the current stack
pointer. These registers can be accessed as the general-purpose register R15. R15 switches between repre-
senting the SPI and SPU depending on the value of the Stack Mode (SM) bit in the PSW.
After reset, the values of the SPI and SPU are undefined.
b0
b31
SPI
SPI
b0
b31
SPU
SPU
2.3.4 Backup PC: BPC (CR6)
The Backup PC (BPC) is used to save the value of the Program Counter (PC) when an EIT occurs. Bit 31 is fixed
to "0".
When an EIT occurs, the register sets either the PC value when the EIT occurred or the PC value for the next
instruction depending on the type of EIT. The BPC value is loaded to the PC when the RTE instruction is
executed. However, the values of the lower 2 bits of the PC are always "00" when returned. (PC always returns
to the word-aligned address.)
After reset, the value of the BPC is undefined.
b0
b31
0
BPC
BPC
32180 Group User’s Manual (Rev.1.0)
2-4
RENESAS [ RENESAS TECHNOLOGY CORP ]
