
Memory and bus architecture
RM0008
Doc ID 13902 Rev 12
Flash access control register (FLASH_ACR)
Address offset: 0x00
Reset value: 0x0000 0030
3.4 Boot
configuration
In the STM32F10xxx, 3 different boot modes can be selected through BOOT[1:0] pins as
shown in
The values on the BOOT pins are latched on the 4th rising edge of SYSCLK after a reset. It
is up to the user to set the BOOT1 and BOOT0 pins after Reset to select the required boot
mode.
The BOOT pins are also re-sampled when exiting from Standby mode. Consequently they
must be kept in the required Boot mode configuration in Standby mode. After this startup
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
Reserved
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Reserved
PRFTBS PRFTBE HLFCYA
LATENCY
r
rw
rw
rw
rw
rw
Bits 31:6 Reserved, must be kept cleared.
Bit 5
PRFTBS
: Prefetch buffer status
This bit provides the status of the prefetch buffer.
0: Prefetch buffer is disabled
1: Prefetch buffer is enabled
Bit 4
PRFTBE
: Prefetch buffer enable
0: Prefetch is disabled
1: Prefetch is enabled
Bit 3
HLFCYA
: Flash half cycle access enable
0: Half cycle is disabled
1: Half cycle is enabled
Bits 2:0
LATENCY
: Latency
These bits represent the ratio of the SYSCLK (system clock) period to the Flash access
time.
000 Zero wait state, if 0 < SYSCLK
≤
24 MHz
001 One wait state, if 24 MHz < SYSCLK
≤
48 MHz
010 Two wait states, if 48 MHz < SYSCLK
≤
72 MHz
Table 9.
Boot modes
Boot mode selection pins
Boot mode
Aliasing
BOOT1
BOOT0
x
0
Main Flash memory
Main Flash memory is selected as boot space
0
1
System memory
System memory is selected as boot space
1
1
Embedded SRAM
Embedded SRAM is selected as boot space