HD64F2149 Datasheet, PDF (188/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

6.4.5 Wait Control
When accessing external space, the MCU can extend the bus cycle by inserting one or more wait
states (T_W). There are three ways of inserting wait states: program wait insertion, pin wait insertion
using the WAIT pin, and a combination of the two.
Program Wait Mode
In program wait mode, the number of T_W states specified by bits WC1 and WC0 are always
inserted between the T₂ and T₃ states when external space is accessed.
Pin Wait Mode
In pin wait mode, the number of T_W states specified by bits WC1 and WC0 are always inserted
between the T₂ and T₃ states when external space is accessed. If the WAIT pin is low at the fall of
ø in the last T₂ or T_W state, another T_W state is inserted. If the WAIT pin is held low, T_W states are
inserted until it goes high.
Pin wait mode is useful for inserting four or more wait states, or for changing the number of T_W
states for different external devices.
Pin Auto-Wait Mode
In pin auto-wait mode, if the WAIT pin is low at the fall of ø in the T₂ state, the number of T_W
states specified by bits WC1 and WC0 are inserted when external space is accessed. No additional
T_W states are inserted even if the WAIT pin remains low. Pin auto-wait mode can be used for an
easy interface to low-speed memory, simply by routing the chip select signal to the WAIT pin.
Figure 6.13 shows an example of wait state insertion timing.
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