
48
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (System Controller and Bus Control)
5.2.2 Address decoder (CE output) settings
As explained in Section 3.6.4, the S1C88409 has a
built-in address decoder that can output up to three
chip enable signals (CE0–CE2) to external devices.
The output terminals and output circuits for CE0–
CE2 are shared with the output ports R30–R32. At
initial reset, they are set as the CE terminals.
Unused CE terminals can be set to general-
purpose output port terminals by writing "0" to the
CE0–CE2 registers.
Table 5.2.2.1 shows the address range assigned to
the chip enable (CE) signals.
External devices can be allocated to an area
selected with an optional chip enable signal.
It is not necessary to continue from a lower
address of the memory space. However in the
MPU mode, the program memory must be as-
signed to CE0.
In the expanded 4M mode, the address range of
each CE signal is fixed.
In the expanded 64K mode, four address ranges
can be selected using the CEMD register (two bits)
according to the memory to be used.
These signals are output only when the correspond-
ing external memory area is accessed and are not
output when the internal memory is accessed.
Furthermore, when the CPU is in standby status
(HALT, SLEEP), all the CE signals go HIGH to
disable external memory access.
Table 5.2.2.1 Address settings of CE0–CE2
CEMD1
1
0
CEMD0
1
0
1
0
Chip size
–
32KB
16KB
8KB
CE0
–
008000H–00EFFFH
007000H–00AFFFH
008000H–009FFFH
CE1
–
00B000H–00EFFFH
00A000H–00BFFFH
CE2
–
00C000H–00DFFFH
CEMD1
1
0
CEMD0
1
0
1
0
Chip size
64KB
32KB
16KB
8KB
CE0
000000H–00EFFFH
000000H–007FFFH
000000H–003FFFH
000000H–001FFFH
CE1
–
008000H–00EFFFH
004000H–007FFFH
002000H–003FFFH
CE2
–
008000H–00BFFFH
004000H–005FFFH
(1) Expanded 64K mode + MCU mode
(2) Expanded 64K mode + MPU mode
CE
signal
CE0
CE1
CE2
Address range
MCU mode
C00000H–FFFFFFH
400000H–7FFFFFH
800000H–BFFFFFH
MPU mode
000000H–00EFFFH, 010000H–3FFFFFH
400000H–7FFFFFH
800000H–BFFFFFH
(3) Expanded 4M minimum/maximum mode
5.2.3 WAIT state settings
In order to guarantee accessing of external low
speed devices during high speed operation, the
S1C88409 is equipped with a WAIT function that
prolongs access time.
The number of wait states to be inserted can be
selected from four values by the WT register (two
bits) as shown in Table 5.2.3.1.
The WAIT states that are set with software are
inserted between the bus cycle states T3 and T4.
Note, however, that WAIT states cannot be in-
serted when an internal register or internal
memory are being accessed and when the CPU
operates with the OSC1 oscillation clock (see
Section 5.4, "Oscillation Circuit").
Consequently, WAIT state settings are invalid in
the single chip mode.
Table 5.2.3.1 Setting the number of WAIT states
Number of inserted states
12
8
4
No wait
WT1
1
0
WT0
1
0
1
0
The length of one state is 1/2 a cycle of the clock.
Refer to Section 3.6.5, "WAIT control", for the
timing chart for WAIT insertion.