HD404459 Datasheet, PDF (9/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
RAM Memory Map
The HD404458 MCU contains a 512-digit × 4-bit RAM area. The HD404459 and HD4074459 MCUs
contain 768-digit × 4-bit RAM areas. Both of these RAM areas consist of a memory register area, a data
area, and a stack area. In addition, an interrupt control bits area, special register area, and register flag area
are mapped onto the same RAM memory space labeled as the RAM-mapped register area. See the RAM
memory map of figure 2.
RAM-Mapped Register Area ($000–$03F):
• Interrupt control bits area ($000–$003)
This area is used for interrupt control bits (figure 3). These bits can be accessed only by RAM bit
manipulation instructions (SEM/SEMD, REM/REMD, and TM/TMD). However, note that not all the
instructions can be used for each bit. For limitations on using the instructions, refer to figure 4.
• Special function register area ($004–$01F, $024–$03F)
This area is used as mode registers and data registers for external interrupts, serial interface,
timer/counters, and as data control registers for I/O ports. See figures 2 and 5. These registers can be
classified into three types: write-only (W), read-only (R), and read/write (R/W). RAM bit manipulation
instructions cannot be used for these registers.
• Register flag area ($020–$023)
This area is used for the DTON, WDON, and other register flags and interrupt control bits (figure 3).
These bits can be accessed only by RAM bit manipulation instructions (SEM/SEMD, REM/REMD, and
TM/TMD). However, note that not all the instructions can be used for each bit. For limitations on using
the instructions, refer to figure 4.
Memory Register (MR) Area ($040–$04F): Consisting of 16 addresses, this area (MR0–MR15) can be
accessed by register-register instructions (LAMR and XMRA). See figure 6.
Data Area ($050–$1FF for HD404458, $050–$2FF for HD404459/HD4074459)
Stack Area ($3C0–$3FF): Used for saving the contents of the program counter (PC), status flag (ST), and
carry flag (CA) at subroutine call (CAL or CALL instruction) and for interrupts. This area can be used as a
16-level nesting subroutine stack in which one level requires four digits. See figure 6 for the data to be
saved and the save conditions.
The program counter is restored by either the RTN or RTNI instruction, but the status and carry flags can
only be restored by the RTNI instruction. Any unused space in this area can be used for data storage.
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