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TC1784
Program Memory Unit (PMU)
User´s Manual
5-24
V1.1, 2011-05
PMU, V1.47
5.6.2.4
Flash Access Control and Performance
The required number of wait states for an initial access to PFlash or DFlash is related to
the maximum operating frequency (including PLL jitter). Because the default after reset
is a worst case setting sufficient for all frequencies, the access times have to be
configured by the user according to the application’s frequency for optimum
performance. This configuration of wait states must be performed via the 4-bit-fields
“WSPFLASH” and “WSDFLASH” in register FCON (Flash Configuration Register, see
) according to the following table.
Note: If the initial access (either instruction or data access) addresses a double-word in
PFlash which is already available in the 256-bit Flash read buffer (either because
of earlier initial access or because of automatic prefetching), the defined number
of wait states (in FCON register) is disabled and the access is performed without
wait state, thus with 0 ns access time (“buffer hit”). In case of prefetch line hit the
number of access cycles is reduced to 1 wait state, if the prefetched read-data line
is already pending before the read buffer.
Table 5-1
Selection of Wait States in Relation to Operating Frequency for Flash
modules with Ta=26 ns
Operating Frequency
1)
1) The maximum operating frequency of a device is documented in its data sheet.
WS for
Initial
Access
WS for
Read Buffer
Hit Access
WS for
Prefetch
Line Hit
150 MHz < f
LMB
≤
180 MHz
5
0
min. 1
112 MHz < f
LMB
≤
150 MHz
4
0
min. 1
75 MHz < f
LMB
≤
112 MHz
3
0
min. 1
37.5 MHz < f
LMB
≤
75 MHz
2
0
min. 1
f
LMB
≤
37.5 MHz
1
0
min. 1
Table 5-2
Selection of Wait States in Relation to Operating Frequency for Flash
modules with Ta=50 ns
Operating Frequency
1)
WS for
Initial
Access
WS for
Read Buffer
Hit Access
WS for
Prefetch
Line Hit
178 MHz < f
LMB
≤
180 MHz
10
0
min. 1
158 MHz < f
LMB
≤
178 MHz
9
0
min. 1
138 MHz < f
LMB
≤
158 MHz
8
0
min. 1
118 MHz < f
LMB
≤
138 MHz
7
0
min. 1
Содержание TC1784
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