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PIC16F57-I/SO 参数 Datasheet PDF下载

PIC16F57-I/SO图片预览
型号: PIC16F57-I/SO
PDF下载: 下载PDF文件 查看货源
内容描述: 基于闪存的8位CMOS微控制器系列 [Flash-Based, 8-Bit CMOS Microcontroller Series]
分类和应用: 闪存微控制器
文件页数/大小: 88 页 / 1373 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC16F5X  
FIGURE 5-7:  
EXTERNAL BROWN-OUT  
PROTECTION CIRCUIT 2  
5.2  
Device Reset Timer (DRT)  
The Device Reset Timer (DRT) provides an 18 ms  
nominal time-out on Reset regardless of the oscillator  
mode used. The DRT operates on an internal RC  
oscillator. The processor is kept in Reset as long as the  
DRT is active. The DRT delay allows VDD to rise above  
VDD min. and for the chosen oscillator to stabilize.  
VDD  
VDD  
R1  
R2  
Q1  
Oscillator circuits, based on crystals or ceramic resona-  
tors, require a certain time after power-up to establish  
a stable oscillation. The on-chip DRT keeps the device  
in a Reset condition for approximately 18 ms after the  
voltage on the MCLR/VPP pin has reached a logic high  
(VIH) level. Thus, external RC networks connected to  
the MCLR input are not required in most cases,  
allowing for savings in cost-sensitive and/or space  
restricted applications.  
MCLR  
40k  
PIC16F5X  
This brown-out circuit is less expensive, although  
less accurate. Transistor Q1 turns off when VDD is  
below a certain level such that:  
The device Reset time delay will vary from chip-to-chip  
due to VDD, temperature and process variation. See  
AC parameters for details.  
R1  
= 0.7V  
VDD •  
R1 + R2  
The DRT will also be triggered upon a Watchdog Timer  
time-out. This is particularly important for applications  
using the WDT to wake the PIC16F5X from Sleep  
mode automatically.  
FIGURE 5-8:  
EXTERNAL BROWN-OUT  
PROTECTION CIRCUIT 3  
5.3  
Reset on Brown-Out  
VDD  
A Brown-out is a condition where device power (VDD)  
dips below its minimum value, but not to zero, and then  
recovers. The device should be reset in the event of a  
Brown-out.  
VDD  
Bypass  
Capacitor  
VDD  
MCP809  
To reset PIC16F5X devices when a Brown-out occurs,  
external Brown-out protection circuits may be built, as  
shown in Figure 5-6, Figure 5-7 and Figure 5-8.  
RST  
MCLR  
PIC16F5X  
VSS  
FIGURE 5-6:  
EXTERNAL BROWN-OUT  
PROTECTION CIRCUIT 1  
This brown-out protection circuit employs  
Microchip Technology’s MCP809 microcontroller  
supervisor. The MCP8XX and MCP1XX families  
of supervisors provide push-pull and open collec-  
tor outputs with both “active-high and active-low”  
Reset pins. There are 7 different trip point  
selections to accommodate 5V and 3V systems.  
VDD  
33k  
VDD  
Q1  
10k  
MCLR  
40k  
PIC16F5X  
This circuit will activate Reset when VDD goes below  
Vz + 0.7V (where Vz = Zener voltage).  
© 2007 Microchip Technology Inc.  
DS41213D-page 27