Datasheet

173
8246B–AVR–09/11
ATtiny2313A/4313
19. Self-Programming
19.1 Features
• Self-Programming Enables MCU to Erase, Write and Reprogram Application Memory
• Efficient Read-Modify-Write Support
• Lock Bits Allow Application Memory to Be Securely Closed for Further Access
19.2 Overview
The device provides a self-programming mechanism for downloading and uploading program
code by the MCU itself. Self-Programming can use any available data interface and associated
protocol to read code and write (program) that code into program memory.
19.3 Lock Bits
Program memory can be protected from internal or external access. See “Lock Bits” on page
178.
19.4 Self-Programming the Flash
Program memory is updated in a page by page fashion. Before programming a page with the
data stored in the temporary page buffer, the page must be erased. The temporary page buffer
is filled one word at a time using SPM and the buffer can be filled either before the Page Erase
command or between a Page Erase and a Page Write operation:
1. Either, fill the buffer before a Page Erase:
a. Fill temporary page buffer
b. Perform a Page Erase
c. Perform a Page Write
2. Or, fill the buffer after Page Erase:
a. Perform a Page Erase
b. Fill temporary page buffer
c. Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be re-written.
The temporary page buffer can be accessed in a random sequence.
It is essential that the page address used in both the Page Erase and Page Write operation is
addressing the same page.
The SPM instruction is disabled by default but it can be enabled by programming the SELFPR-
GEN fuse (to “0”).
19.4.1 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7Z6Z5Z4Z3Z2Z1Z0
76543210