2.9 Basic Operational Timing
2.9.1 Overview
The H8/300H CPU operates according to the system clock (ø). The interval from one rise of the
system clock to the next rise is referred to as a “state.” A memory cycle or bus cycle consists of
two or three states. The CPU uses different methods to access on-chip memory, the on-chip
supporting modules, and the external address space. Access to the external address space can be
controlled by the bus controller.
2.9.2 On-Chip Memory Access Timing
On-chip memory is accessed in two states. The data bus is 16 bits wide, permitting both byte and
word access. Figure 2-15 shows the on-chip memory access cycle. Figure 2-16 indicates the pin
states.
Figure 2-15 On-Chip Memory Access Cycle
T state
Bus cycle
Internal address bus
Internal read signal
Internal data bus
(read access)
Internal write signal
Internal data bus
(write access)
ø
1
T state
2
Read data
Address
Write data
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