UPD784026 Renesas Electronics Corporation., UPD784026 Datasheet - Page 96

• Manufacturer Part Number: UPD784026
• Description: 16/8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

(3) Operating precautions
56
Switching the RSS bit has the same effect as having two register sets. However, when writing a program, care must be
taken to ensure that the static program code and dynamic RSS bit changes at the time of program execution always coincide.
Also, a program that sets RSS to 1 cannot be used by a program that uses the context switching function, and therefore
program usability is poor. Moreover, since different registers are used with the same name, program readability is poor and
debugging is difficult. Therefore, if it is necessary to set RSS to 1, these disadvantages must be fully taken into consideration
when writing a program.
A register not specified by the RSS bit can be accessed by writing its absolute name.
• If A, X, B, C, AX or BC is written in an instruction for which r, r’, rp and rp’ are specified in the operand column, the A, X,
• If R0 to R7 or RP0 to RP4 is written as r, r’, rp or rp’ in the operand column, an operation code in accordance with that
• R1, R3, R2 or R5, R7, R6 cannot be used for registers A, B and C used in indexed addressing and based indexed
B, C, AX and BC instructions generate an operation code that specifies the following registers according to the operand
of the RA78K4 RSS pseudo-instruction.
specification is output (an operation code for which A or AX is directly entered in the operand column is not output.)
addressing.
CHAPTER 3 CPU ARCHITECTURE
Register
A
X
B
C
AX
BC
RSS = 0
R1
R0
R3
R2
RP0
RP1
RSS = 1
R5
R4
R7
R6
RP2
RP3