HD404459 Datasheet, PDF (107/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
ROM Addressing Modes and the P Instruction
The MCU has four ROM addressing modes (figure 85).
Direct Addressing Mode: A program can branch to any address in ROM memory space by executing the
JMPL, BRL, or CALL instruction. Each of these instructions replaces the 14 program counter bits (PC₁₃–
PC₀) with 14-bit immediate data.
Current Page Addressing Mode: The MCU has 64 pages of ROM with 256 words per page. A program
can branch to any address in the current page by executing the BR instruction. This instruction replaces the
eight low-order bits of the program counter (PC₇–PC₀) with eight-bit immediate data. If the BR instruction
is on a page boundary (address 256n + 255), executing that instruction transfers the PC contents to the next
physical page (figure 87). This means that the execution of the BR instruction on a page boundary will
make the program branch to the next page.
Note that the HMCS400-series cross macroassembler has an automatic paging feature for ROM pages.
Zero-Page Addressing Mode: A program can branch to the zero-page subroutine area located at $0000–
$003F by executing the CAL instruction. When the CAL instruction is executed, 6 bits of immediate data
are placed in the six low-order bits of the program counter (PC₅–PC₀), and 0s are placed in the eight high-
order bits (PC₁₃–PC₆).
Table Data Addressing Mode: A program can branch to an address determined by the contents of four-bit
immediate data, the accumulator, and the B register by executing the TBR instruction.
P Instruction: ROM data addressed in table data addressing mode can be referenced with the P instruction
(figure 86). If bit 8 of the ROM data is 1, eight bits of ROM data are written to the accumulator and the B
register. If bit 9 is 1, eight bits of ROM data are written to the R1 and R2 port output registers. If both bits 8
and 9 are 1, ROM data is written to the accumulator and the B register, and also to the R1 and R2 port
output registers at the same time.
The P instruction has no effect on the program counter.
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