6.3.2 Chip Select Signals
For each of areas 0 to 7, the H8/3048 Series can output a chip select signal (CS
0
to CS
7
) that goes
low to indicate when the area is selected. Figure 6-3 shows the output timing of a CS
n
signal
(n = 0 to 7).
Output of CS
0
to CS
3
: Output of CS
0
to CS
3
is enabled or disabled in the data direction register
(DDR) of the corresponding port.
In the expanded modes with on-chip ROM disabled, a reset leaves pin CS
0
in the output state and
pins CS
1
to CS
3
in the input state. To output chip select signals CS
1
to CS
3
, the corresponding
DDR bits must be set to 1. In the expanded modes with on-chip ROM enabled, a reset leaves pins
CS
0
to CS
3
in the input state. To output chip select signals CS
0
to CS
3
, the corresponding DDR
bits must be set to 1. For details see section 9, I/O Ports.
Output of CS
4
to CS
7
: Output of CS
4
to CS
7
is enabled or disabled in the chip select control
register (CSCR). A reset leaves pins CS
4
to CS
7
in the input state. To output chip select signals
CS
4
to CS
7
, the corresponding CSCR bits must be set to 1. For details see section 9, I/O Ports.
Figure 6-3 CS
n
Output Timing (n = 0 to 7)
When the on-chip ROM, on-chip RAM, and on-chip registers are accessed, CS
0
and CS
7
remain
high. The CS
n
signals are decoded from the address signals. They can be used as chip select
signals for SRAM and other devices.
Address
bus
n
External address in area n
ø
CS
123
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