Electronic Components Datasheet Search |
|
P83C851FHB Datasheet(PDF) 9 Page - NXP Semiconductors |
|
P83C851FHB Datasheet(HTML) 9 Page - NXP Semiconductors |
9 / 22 page Philips Semiconductors Product specification 80C851/83C851 CMOS single-chip 8-bit microcontroller with on-chip EEPROM 1998 Jul 03 9 Security Facilities EEPROM Protection The EEPROM is protected using four security bits which are contained in an extra EEPROM byte at address 8000H (EADRH/EADRL). They can be set or cleared by software. To activate the EEPROM protection, the program sequence in byte mode must be as follows: MOV EADRH, #80H MOV EADRL, #00H MOV EDAT, #FFH If two or more of these bits are reset, SB = 0, the security mode is disabled and the EEPROM is not protected. If three or four bits are set, SB = 1 and the EA mode differs from the internal access mode. In this case, access to the EEPROM is only possible in one mode regardless of how the external access mode is reached (by pulling the EA pin low or by passing the 4K boundary). For SB = 1 and “external access” only, the “block erase” mode is enabled. The program sequence has to be as follows: MOV EADRH, #80H (security byte address) MOV EADRL, #00H (security byte address) MOV ECNTRL, #0AH (block erase mode) MOV EDAT, #xxH (start block erase) All 256 data bytes, the security bits, and SB will be cleared after completing this mode (EWP = 0). SB will also be affected in byte mode when writing to the security byte (not for SB = 1 and “external access”). Figure 3 illustrates the access to SB. ROM Code Protection Since the external access mode can only be selected by pulling the EA pin low during reset, it is not possible to read the internal program memory using the MOVC instruction while executing external program memory. Furthermore, it is not possible to change this mode to internal access within the MOVC cycle. Additionally, a mask-programmable ROM code protection facility is available. When the program memory passes the 4K boundary using both the internal and external ROMs, it is not possible to access the internal ROM from the external program memory if the mask-programmable ROM security bit is set. An access to the lower 4K bytes of program memory using the MOVC instruction is only possible while executing internal program memory. Also the verification mode (test-mode which writes the ROM contents to a port for comparison with a reference code) is not implemented for security reasons. A different test-mode is implemented for test purposes. This mode allows every bit to be tested. However, the internal code cannot be accessed via a port. RESET RESET EADRH EADRL EEPROM EA EDATA L n EAQ RESET REGISTERS EADRH AND EADRL CONTAIN THE ADDRESS OF THE SECURITY BYTE SECURITY BYTE ADDRESS AND BLOCK ERASE FINISHED SECURITY BYTE ADDRESS AND BYTE MODE FINISHED RESET SB SB = 1 EXTERNAL ACCESS INHIBIT ‘READ DATA REGISTER’ INHIBIT ‘WRITE DATA REGISTER’ EXCEPT (ECNTRL) = BLOCK ERASE NO NO YES YES Figure 3. EEPROM Protection (Functional and Flowchart) 8 |
Similar Part No. - P83C851FHB |
|
Similar Description - P83C851FHB |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |