UPD784026 Renesas Electronics Corporation., UPD784026 Datasheet - Page 94

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

3.7.3 Use of RSS Bit
to 1. This explanation can be skipped if the RSS bit is fixed at 0.
R4 to R7 (RP2, RP3) as well. Effective use of this bit enables efficient programs to be written in terms of program size and
program execution.
should only be set to 1 when a 78K/III series program is used.
so that it does not set the RSS bit to 1.
(1) RSS bit recommendations
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Basically, the RSS bit should be fixed at 0 at all times.
The following explanation refers to the case where a 78K/III series program is used, and the program used sets the RSS bit
The RSS bit is provided to allow the functions of A (R1), X (R0), B (R3), C (R2), AX (RP0) and BC (RP1) to be used by registers
However, careless use can result in unforeseen problems. Therefore, the RSS bit should always be set to 0. The RSS bit
Use of the RSS bit set to 0 in all programs will improve programming and debugging efficiency.
Even when using a program in which the RSS bit set to 1 is used, it is recommended that the program be amended if possible
The registers used in these cases are switched as follows according to the RSS bit.
• Registers used by instructions for which the A, X, B, C and AX registers are directly entered in the operand column of
• Registers specified as implied by instructions that use the A, AX, B and C registers by means of implied addressing
• Registers used in addressing by instructions that use the A, B and C registers in indexed addressing and based indexed
the operation list (see 25.2.)
addressing
•
•
When RSS = 0
A R1, X R0, B R3, C R2, AX RP0, BC RP1
When RSS = 1
A R5, X R4, B R7, C R6, AX RP2, BC RP3
CHAPTER 3 CPU ARCHITECTURE