參數資料
型號: PIC18LF2450T-I/SO
廠商: Microchip Technology
文件頁數: 85/143頁
文件大?。?/td> 0K
描述: IC PIC MCU FLASH 8KX16 28SOIC
標準包裝: 1,600
系列: PIC® 18F
核心處理器: PIC
芯體尺寸: 8-位
速度: 48MHz
連通性: UART/USART,USB
外圍設備: 欠壓檢測/復位,HLVD,POR,PWM,WDT
輸入/輸出數: 23
程序存儲器容量: 16KB(8K x 16)
程序存儲器類型: 閃存
RAM 容量: 768 x 8
電壓 - 電源 (Vcc/Vdd): 2 V ~ 5.5 V
數據轉換器: A/D 10x10b
振蕩器型: 內部
工作溫度: -40°C ~ 85°C
封裝/外殼: 28-SOIC(0.295",7.50mm 寬)
包裝: 帶卷 (TR)
PIC18F2450/4450
DS39760A-page 44
Advance Information
2006 Microchip Technology Inc.
4.4
Brown-out Reset (BOR)
PIC18F2450/4450 devices implement a BOR circuit
that provides the user with a number of configuration
and power-saving options. The BOR is controlled by
the
BORV1:BORV0
and
BOREN1:BOREN0
Configuration bits. There are a total of four BOR
configurations which are summarized in Table 4-1.
The BOR threshold is set by the BORV1:BORV0 bits. If
BOR is enabled (any values of BOREN1:BOREN0
except ‘00’), any drop of VDD below VBOR (parameter
D005, Section 267 “DC Characteristics: Supply
Voltage”) for greater than TBOR (parameter 35,
Table 21-10) will reset the device. A Reset may or may
not occur if VDD falls below VBOR for less than TBOR.
The chip will remain in Brown-out Reset until VDD rises
above VBOR.
If the Power-up Timer is enabled, it will be invoked after
VDD rises above VBOR; it then will keep the chip in
Reset
for
an
additional
time
delay,
TPWRT
(parameter 33, Table 21-10). If VDD drops below VBOR
while the Power-up Timer is running, the chip will go
back into a Brown-out Reset and the Power-up Timer
will be initialized. Once VDD rises above VBOR, the
Power-up Timer will execute the additional time delay.
BOR
and
the
Power-on
Timer
(PWRT)
are
independently configured. Enabling BOR Reset does
not automatically enable the PWRT.
4.4.1
SOFTWARE ENABLED BOR
When BOREN1:BOREN0 = 01, the BOR can be
enabled or disabled by the user in software. This is
done with the control bit, SBOREN (RCON<6>).
Setting SBOREN enables the BOR to function as
previously described. Clearing SBOREN disables the
BOR entirely. The SBOREN bit operates only in this
mode; otherwise, it is read as ‘0’.
Placing the BOR under software control gives the user
the additional flexibility of tailoring the application to its
environment without having to reprogram the device to
change BOR configuration. It also allows the user to
tailor device power consumption in software by eliminat-
ing the incremental current that the BOR consumes.
While the BOR current is typically very small, it may have
some impact in low-power applications.
4.4.2
DETECTING BOR
When BOR is enabled, the BOR bit always resets to ‘0’
on any BOR or POR event. This makes it difficult to
determine if a BOR event has occurred just by reading
the state of BOR alone. A more reliable method is to
simultaneously check the state of both POR and BOR.
This assumes that the POR bit is reset to ‘1’ in software
immediately after any POR event. IF BOR is ‘0’ while
POR is ‘1’, it can be reliably assumed that a BOR event
has occurred.
4.4.3
DISABLING BOR IN SLEEP MODE
When BOREN1:BOREN0 = 10, the BOR remains
under hardware control and operates as previously
described. Whenever the device enters Sleep mode,
however, the BOR is automatically disabled. When the
device returns to any other operating mode, BOR is
automatically re-enabled.
This mode allows for applications to recover from
brown-out situations, while actively executing code,
when the device requires BOR protection the most. At
the same time, it saves additional power in Sleep mode
by eliminating the small incremental BOR current.
TABLE 4-1:
BOR CONFIGURATIONS
Note:
Even when BOR is under software control,
the BOR Reset voltage level is still set by
the BORV1:BORV0 Configuration bits. It
cannot be changed in software.
BOR Configuration
Status of
SBOREN
(RCON<6>)
BOR Operation
BOREN1
BOREN0
00
Unavailable
BOR disabled; must be enabled by reprogramming the Configuration bits.
01
Available
BOR enabled in software; operation controlled by SBOREN.
10
Unavailable
BOR enabled in hardware in Run and Idle modes, disabled during
Sleep mode.
11
Unavailable
BOR enabled in hardware; must be disabled by reprogramming the
Configuration bits.
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