Datasheet
XC164-32
Derivatives
Electrical Parameters
Data Sheet 67 V1.1, 2006-08
4.4.2 On-chip Flash Operation
The XC164CS’s Flash module delivers data within a fixed access time (see Table 17).
Accesses to the Flash module are controlled by the PMI and take 1 + WS clock cycles,
where WS is the number of Flash access waitstates selected via bitfield WSFLASH in
register IMBCTRL. The resulting duration of the access phase must cover the access
time
t
ACC
of the Flash array. Therefore, the required Flash waitstates depend on the
available speed grade as well as on the actual system frequency.
Note: The Flash access waitstates only affect non-sequential accesses. Due to
prefetching mechanisms, the performance for sequential accesses (depending on
the software structure) is only partially influenced by waitstates.
In typical applications, eliminating one waitstate increases the average
performance by 5% … 15%.
Example: For an operating frequency of 40 MHz (clock cycle = 25 ns), Standard devices
must be operated with 2 waitstates: ((2 + 1)
× 25 ns) ≥ 70 ns.
Grade A devices can be operated with 1 waitstate: ((1 + 1)
× 25 ns) ≥ 50 ns.
Table 18 indicates the interrelation of waitstates, system frequency, and speed grade.
Note: The maximum achievable system frequency is limited by the properties of the
respective derivative, i.e. 40 MHz (or 20 MHz for xxx-32F20F devices).
Table 17 Flash Characteristics
(Operating Conditions apply)
Parameter Symbol Limit Values Unit
Min. Typ. Max.
Flash module access time (Standard) t
ACC
CC – – 70
1)
1) The actual access time is also influenced by the system frequency, so the frequency ranges are not fully linear.
See
Table 18.
ns
Flash module access time (Grade A)
t
ACC
CC – – 50
1)
ns
Programming time per 128-byte block
t
PR
CC – 2
2)
2) Programming and erase time depends on the system frequency. Typical values are valid for 40 MHz.
5ms
Erase time per sector
t
ER
CC – 200
2)
500 ms
Table 18 Flash Access Waitstates
Required Waitstates Frequency Range for
Standard Flash Speed
Frequency Range for
Flash Speed Grade A
0 WS (WSFLASH = 00
B
) f
CPU
≤ 16 MHz f
CPU
≤ 20 MHz
1 WS (WSFLASH = 01
B
) f
CPU
≤ 28 MHz f
CPU
≤ 40 MHz
2 WS (WSFLASH = 10
B
) f
CPU
≤ 40 MHz f
CPU
≤ 40 MHz