4 MEMORY AND BUS
4.2 Bus Access Cycle
The CPU uses the system clock for bus access operations. First, "Bus access cycle," "Device size," and "Access
size" are defined as follows:
• Bus access cycle: One system clock period = 1 cycle
• Device size:
Bit width of the memory and peripheral circuits that can be accessed in one cycle
• Access size:
Access size designated by the CPU instructions (e.g., LDR Rt, [Rn] → 32-bit data transfer)
Table 4.2.1 lists numbers of bus access cycles by different device size and access size. The peripheral circuits can
be accessed with an 8- or 16-bit instruction.
4.3 Flash Memory
The Flash memory is used to store application programs and data. Address 0x0 in the Flash area is defined as the
vector table base address by default, therefore a vector table must be located beginning from this address. For more
information on the vector table, refer to "Vector Table" in the "Interrupt" chapter.
4.3.1 Flash Memory Pin
Table 4.3.1.1 shows the Flash memory pin.
Pin name
V
PP
4.3.2 Flash Bus Access Cycle Setting
There is a limit of frequency to access the Flash memory with no wait cycle, therefore, the number of bus access
cycles for reading must be changed according to the system clock frequency. The number of bus access cycles for
reading can be configured using the FLASHCWAIT.RDWAIT[1:0] bits. Select a setting for higher frequency than
the system clock.
4.3.3 Flash Programming
The Flash memory supports on-board programming, so it can be programmed using a flash loader. The V
is supplied from the internal voltage booster.
Be sure to connect C
between the V
VPP
Notes: • When programming the Flash memory, 2.2 V or more V
• Be sure to avoid using the V
4-2
Table 4.2.1 Number of Bus Access Cycles
Device size
Access size
8 bits
16 bits
32 bits
Table 4.3.1.1 Flash Memory Pin
I/O
Initial status
P
–
and V
pins for generating the voltage using the internal power supply.
SS
PP
pin output for driving external circuits.
PP
Seiko Epson Corporation
Number of bus access
cycles
8 bits
16 bits
32 bits
8 bits
16 bits
32 bits
8 bits
16 bits
32 bits
Flash programming power supply
voltage is required.
DD
1
2
4
1
1
2
1
1
1
Function
PP
S1C31D41 TECHNICAL MANUAL
voltage
(Rev. 1.1)