D12320VF25IV Datasheet, PDF (213/1304 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 6 Bus Controller
6.4.5 Wait Control
When accessing external space, the chip can extend the bus cycle by inserting one or more wait
states (T_w). There are two ways of inserting wait states: program wait insertion and pin wait
insertion using the WAIT pin.
Program Wait Insertion: From 0 to 3 wait states can be inserted automatically between the T₂
state and T₃ state on an individual area basis in 3-state access space, according to the settings of
WCRH and WCRL.
Pin Wait Insertion: Setting the WAITE bit in BCRL to 1 enables wait insertion by means of the
WAIT pin. When external space is accessed in this state, program wait insertion is first carried out
according to the settings in WCRH and WCRL. Then, if the WAIT pin is low at the falling edge of
φ in the last T₂ or T_w state, a T_w state is inserted. If the WAIT pin is held low, T_w states are
inserted until it goes high.
This is useful when inserting four or more T_w states, or when changing the number of T_w states for
different external devices.
The WAITE bit setting applies to all areas. The WAITPS bit can be used to change the WAIT
input pin from PF₂ to P5₃. To make this change, select the input pin with the WAITPS bit, then set
the WAITE bit.
Rev.6.00 Sep. 27, 2007 Page 181 of 1268
REJ09B0220-0600