HD404814FS datasheet(13/100 Pages) RENESAS

13 / 100 page

HD404818 Series

RAM Memory Map

The MCU also contains a 1,184-digit

× 4-bit RAM as the data and stack area. In addition to these areas,

interrupt control bits and special function registers are mapped on the RAM memory space. The RAM

memory map (figure 2) is described in the following paragraphs.

Interrupt Control Bits Area ($000 to $003): The interrupt control bits area (figure 3) is used for interrupt

control. It is accessible only by RAM bit manipulation instructions. However, the interrupt request flag

cannot be set by software. The RSP bit is used only to reset the stack pointer.

Special Function Registers Area ($004 to $01F, $024 to $03F): The special function registers are the

mode or data registers for the serial interface, timer/counters, LCD, and the data control registers for the

I/O ports. These registers are classified into three types: write-only, read-only, and read/write as shown in

figure 2.

The SEM/REM and SEMD/REMD instructions are available for the LCD control register (LCR).

Other registers cannot be accessed by RAM bit manipulation instructions.

registers accessible by the RAM bit manip ula tion instruction.

The WDON flag can only be set, and only by the SEM/SEMD instruction.

The DTON flag can be set, reset, and tested by the SEM/SEMD, REM/REMD, and TMD instructions. Note

that the DTON flag is active only in subactive mode, and is normally reset in active mode.

LCD Data Area ($050 to $06F): Locations $050 to $06F store the LCD data which is automatically

transmitted to the segment driver as display data. The LCD is illuminated with 1s and faded with 0s. This

area can be used as a data area.

Data Area ($040 to $2CF, $100 to $2CF; Bank 0/1): The 16 digits of $040 through $04F are called

memory registers (MR) and are accessible by the LAMR and XMRA instructions (figure 4). 464 digits of

$100 through $2CF are selected as bank 0 or 1 depending on the value of the V register.

Stack Area ($3C0 to $3FF): Locations $3C0 through $3FF are reserved for LIFO stacks to save the

contents of the program counter (PC), status flag (ST), and carry flag (CA) when subroutine calls (CAL or

CALL instruction) and interrupts are processed. This area can be used as a 16-level nesting stack in which

one level requires 4 digits.

Figure 4 shows the save condition. The program counter is restored by the RTN and RTNI instructions. The

status and carry flags are restored only by the RTNI instruction. This area, when not used as a stack, is

available as a data area.

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