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PIC18F4520-I/PT 参数 Datasheet PDF下载

PIC18F4520-I/PT图片预览
型号: PIC18F4520-I/PT
PDF下载: 下载PDF文件 查看货源
内容描述: 28 /40/ 44引脚增强型闪存微控制器与10位A / D和纳瓦技术 [28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology]
分类和应用: 闪存微控制器
文件页数/大小: 412 页 / 6898 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC18F2420/2520/4420/4520  
The long write is necessary for programming the inter-  
6.5  
Writing to Flash Program Memory  
nal Flash. Instruction execution is halted while in a long  
write cycle. The long write will be terminated by the  
internal programming timer.  
The minimum programming block is 16 words or  
32 bytes. Word or byte programming is not supported.  
Table writes are used internally to load the holding  
registers needed to program the Flash memory. There  
are 32 holding registers used by the table writes for  
programming.  
The EEPROM on-chip timer controls the write time.  
The write/erase voltages are generated by an on-chip  
charge pump, rated to operate over the voltage range  
of the device.  
Since the Table Latch (TABLAT) is only a single byte,  
the TBLWT instruction may need to be executed  
32 times for each programming operation. All of the  
table write operations will essentially be short writes  
because only the holding registers are written. At the  
end of updating the 32 holding registers, the EECON1  
register must be written to in order to start the  
programming operation with a long write.  
Note:  
The default value of the holding registers on  
device Resets and after write operations is  
FFh. A write of FFh to a holding register  
does not modify that byte. This means indi-  
vidual bytes of program memory may be  
modified, provided that the change does not  
attempt to change any bit from a ‘0’ to a ‘1’.  
When modifying individual bytes, it is not  
necessary to load all 32 holding registers  
before executing a write operation.  
FIGURE 6-5:  
TABLE WRITES TO FLASH PROGRAM MEMORY  
TABLAT  
Write Register  
8
8
8
8
TBLPTR = xxxxx0  
TBLPTR = xxxxx1  
TBLPTR = xxxxx2  
TBLPTR = xxxx3F  
Holding Register  
Holding Register  
Holding Register  
Holding Register  
Program Memory  
8. Disable interrupts.  
6.5.1  
FLASH PROGRAM MEMORY WRITE  
SEQUENCE  
9. Write 55h to EECON2.  
10. Write 0AAh to EECON2.  
The sequence of events for programming an internal  
program memory location should be:  
11. Set the WR bit. This will begin the write cycle.  
12. The CPU will stall for duration of the write (about  
2 ms using internal timer).  
1. Read 64 bytes into RAM.  
2. Update data values in RAM as necessary.  
13. Re-enable interrupts.  
3. Load Table Pointer register with address being  
erased.  
14. Verify the memory (table read).  
This procedure will require about 6 ms to update one  
row of 64 bytes of memory. An example of the required  
code is given in Example 6-3.  
4. Execute the row erase procedure.  
5. Load Table Pointer register with address of first  
byte being written.  
6. Write the 32 bytes into the holding registers with  
auto-increment.  
Note:  
Before setting the WR bit, the Table  
Pointer address needs to be within the  
intended address range of the 32 bytes in  
the holding register.  
7. Set the EECON1 register for the write operation:  
• set EEPGD bit to point to program memory;  
• clear the CFGS bit to access program memory;  
• set WREN to enable byte writes.  
© 2008 Microchip Technology Inc.  
DS39631E-page 79  
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