Datasheet

Section 2 CPU
Page 58 of 1408 R01UH0309EJ0500 Rev. 5.00
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
Bit Bit Name Initial Value R/W Description
2 Z Undefined R/W Zero Flag
Set to 1 to indicate zero data, and cleared to 0 to
indicate non-zero data.
1 V Undefined R/W Overflow Flag
Set to 1 when an arithmetic overflow occurs, and
cleared to 0 otherwise.
0 C 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.
2.4.5 Multiply-Accumulate Register (MAC)
This 64-bit register stores the results of multiply-and-accumulate operations. It consists of two 32-
bit registers denoted MACH and MACL. The lower 10 bits of MACH are valid; the upper bits are
a sign extension.
2.4.6 Initial Values of CPU Internal Registers
When the reset exception handling loads the start address from the vector address, PC is
initialized, the T bit in EXR is cleared to 0, and the I bits in EXR and CCR are set to 1. However,
the general registers and the other CCR bits are not initialized. The initial value of SP (ER7) is
undefined. SP should therefore be initialized by using the MOV.L instruction immediately after a
reset.