Datasheet

Section 6 Bus Controller
Rev. 4.00 Jun 06, 2006 page 145 of 1004
REJ09B0301-0400
6.3.4 I/O Select Signal
In the H8S/2138 Group and H8S/2134 Group, an I/O select signal (IOS) can be output, with the
signal output going low when the designated external space is accessed.
Figure 6.2 shows an example of IOS signal output timing.
φ
Address bus
IOS
T
1
T
2
T
3
Bus cycle
External address in IOS set range
Figure 6.2 IOS
IOSIOS
IOS Signal Output Timing
Enabling or disabling of IOS signal output is controlled by the setting of the IOSE bit in SYSCR.
In expanded mode, this pin operates as the AS output pin after a reset, and therefore the IOSE bit
in SYSCR must be set to 1 in order to use this pin as the IOS signal output. See section 8, I/O
Ports, for details.
The range of addresses for which the IOS signal is output can be set with bits IOS1 and IOS0 in
BCR. The IOS signal address ranges are shown in table 6.4.
Table 6.4 IOS
IOSIOS
IOS Signal Output Range Settings
IOS1 IOS0 IOS
IOSIOS
IOS Signal Output Range
0 0 H'(FF)F000 to H'(FF)F03F
1 H'(FF)F000 to H'(FF)F0FF
1 0 H'(FF)F000 to H'(FF)F3FF
1 H'(FF)F000 to H'(FF)FE4F
*
(Initial value)
Note: * In the H8S/2138 F-ZTAT A-mask version, the address range is from H'(FF)F000 to
H'(FF)F7FF.