Bus Specifications - Hitachi H8/3006 Hardware Manual

6.3.2

Bus Specifications

The external space bus specifications consist of three elements: (1) bus width, (2) number of
access states, and (3) number of program wait states.
The bus width and number of access states for on-chip memory and registers are fixed, and are not
affected by the bus controller.
Bus Width: A bus width of 8 or 16 bits can be selected with ABWCR. An area for which an 8-bit
bus is selected functions as an 8-bit access space, and an area for which a 16-bit bus is selected
functions as a16-bit access space.
If all areas are designated for 8-bit access, 8-bit bus mode is set; if any area is designated for 16-
bit access, 16-bit bus mode is set.
Number of Access States: Two or three access states can be selected with ASTCR. An area for
which two-state access is selected functions as a two-state access space, and an area for which
three-state access is selected functions as a three-state access space.
DRAM space is accessed in four states regardless of the ASTCR settings.
When two-state access space is designated, wait insertion is disabled.
Number of Program Wait States: When three-state access space is designated in ASTCR, the
number of program wait states to be inserted automatically is selected with WCRH and WCRL.
From 0 to 3 program wait states can be selected.
When ASTCR is cleared to 0 for DRAM space, a program wait (T -T wait) is not inserted.
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Also, no program wait is inserted in burst ROM space burst cycles.
Table 6.3 shows the bus specifications for each basic bus interface area.
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