
46
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (System Controller and Bus Control)
5.2 System Controller
and Bus Control
The system controller is a control unit which sets
the bus mode according to the system configura-
tion such as the external memory.
The software can set the following items to control
the system.
(1) Bus mode (CPU mode)
(2) Chip enable (CE) signal output
(3) WAIT state for external memory
The following explains the settings.
5.2.1 Bus mode settings
The S1C88409 has four bus modes as shown in
Section 3.5.2, "Bus mode". The bus mode should be
set according to the capacity of the memory
expanded.
The bus mode can be set by writing to the BSMD
register (two bits) as shown in Table 5.2.1.1.
At initial reset, the bus mode is set as follows:
MCU mode:
At initial reset, the S1C88409 is set in the single
chip mode.
Accordingly, the system is activated by the pro-
gram written to the internal ROM in the MCU
mode even if the external memory has been
expanded.
When the external memory has been expanded, set
the corresponding bus mode with the initial
routine written in the internal ROM.
MPU mode:
When the MPU mode is used, the expanded mode
(expanded 64K mode, expanded 4M minimum
mode or expanded 4M maximum mode) at initial
reset, has to have been previously selected by the
mask option.
Set it according to the system configuration.
The function of I/O terminals is set as shown in
Table 5.2.1.2 depending on the mode selection.
Table 5.2.1.1 Bus mode settings
1
0
Expanded 4M maximum mode
Expanded 4M minimum mode
Expanded 64K mode
Single chip mode (MCU)
Optional setting of one of the expanded modes (MPU)
Bus mode
Setting value
BSMD1
1
0
1
0
BSMD0
Configuration of external memory
ROM+RAM>64K bytes (Program>64K bytes)
ROM+RAM>64K bytes (Program
≤64K bytes)
ROM+RAM
≤64K bytes
None
See above
The single chip mode can be set only when the S1C88409 is used in the MCU mode.
In the MPU mode, the single chip mode cannot be set since the MPU mode does not use the internal
ROM.
When using the S1C88409 in the MPU mode, it is necessary to select the bus mode at initial reset (and
when the BSMD register is set to "0") by mask option from the three types of expanded modes:
expanded 64K mode, expanded 4M minimum mode and expanded 4M maximum mode.
Select the expanded 4M maximum mode, when the MPU mode is not used.