H83802 datasheet(86/555 Pages) RENESAS

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Section 2 CPU

Rev. 6.00 Mar 15, 2005 page 36 of 502

REJ09B0024-0600

Bit

Bit Name

Initial

Value

R/W

Description

Undefined

R/W

Carry Flag

Set to 1 when a carry occurs, and cleared to 0

otherwise. Used by:

• Add instructions, to indicate a carry

• Subtract instructions, to indicate a borrow

• Shift and rotate instructions, to indicate a carry

The carry flag is also used as a bit accumulator by bit

manipulation instructions.

Some instructions leave flag bits unchanged.

For the action of each instruction on the flag bits, refer to H8/300L Series Programming Manual.

2.3.4

Initial Register Values

When the CPU is reset, the program counter (PC) is initialized to the value stored at address

H'0000 in the vector table, and the I bit in the CCR is set to 1. The other CCR bits and the general

registers are not initialized. In particular, the initial value of the stack pointer (R7) is undefined.

The stack pointer should be initialized by software, by the first instruction executed after a reset.

2.4

Data Formats

The H8/300L CPU can process 1-bit data, 4-bit (BCD) data, 8-bit (byte) data, and 16-bit (word)

data. Bit manipulation instructions operate on 1-bit data specified as bit n in a byte operand (n = 0,

1, 2, ..., 7).

All arithmetic and logic instructions except ADDS and SUBS can operate on byte data. The

MOV.W, ADD.W, SUB.W, CMP.W, ADDS, SUBS, MULXU (8 bits

× 8 bits), and DIVXU (16

bits ÷ 8 bits) instructions operate on word data.

The DAA and DAS decimal-adjust instructions treat byte data as two digits of 4-bit BCD data.

2.4.1

General Register Data Formats

Figure 2.4 shows the data formats in general registers.

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