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CONNECTION WITH EXTERNAL DEVICES
7902 Group User’s Manual
3-10
s External bus cycle select bit 1 (bit 0)
The combination of this bit and the external bus cycle select bit 0 (bits 2, 3 at address 5E16) selects
the bus cycle at access to the external areas except for areas CS0 to CS3. (Refer to section “3.2.2
External bus operations.”)
s RDY input select bit (bit 2)
This bit selects whether the RDY input is enabled or not. Setting this bit to “1” enables the RDY
control at access to the external areas except for areas CS0 to CS3.
To validate the RDY control at the access to any of areas CS0 to CS3, set this bit to “1” and clear
the corresponding RDY control bit for areas CS0 to CS3 (bit 3 at address 8016, 8216, 8416, or 8616)
to “0.”
s Recovery cycle insert select bit (bit 4)
This bit decides whether recovery cycles are inserted or not at access to the external areas except
for areas CS0 to CS3. Setting this bit to “1” inserts such recovery cycles as 1 or 2 cycles of
φ1 after
the bus cycle for access to an external area. The number of recovery cycles to be inserted is
specified by the recovery-cycle-insert number select bit (bit 6). Insertion of recovery cycles allows
devices with longer output disable time at read to be connected without using bus buffers.
Since addresses are maintained throughout recovery cycles, devices requiring longer address hold
time can easily be connected; on the other hand, by inserting 2 recovery cycles to extend the data
hold time at write by 1 cycle of
φ1, devices requiring longer data hold time can also be connected.
(Refer to section “3.2.2 External bus operations.”)
s Recovery-cycle-insert number select bit (bit 6)
This bit selects the number of recovery cycles to be inserted. 1 and 2 cycles are selectable.
The number of recovery cycles selected by this bit is valid for all of the external areas including
areas CS0 to CS3.
To insert recovery cycles, each recovery cycle insert select bit for each area (bit 4 at address 5F 16
and bit 6 at address 8016, 8216, 8416, or 8616) must be set to “1.”
Make sure that a program to be used to change this bit’s contents is allocated in the internal area.
3.2 Chip select wait controller