11. Programming The Flash
The AT89C2051 is shipped with the 2K bytes of on-chip PEROM code memory array in the erased state (i.e., contents = FFH) and ready to be programmed. The code memory array is pro-grammed one byte at a time. Once the array is programmed, to re-program any non-blank byte, the entire memory array needs to be erased electrically.Internal Address Counter: The AT89C2051 contains an internal PEROM address counter which is always reset to 000H on the rising edge of RST and is advanced by applying a positive going pulse to pin XTAL1.Programming Algorithm: To program the AT89C2051, the following sequence is recommended.
1. Power-up sequence:
Apply power between VCC and GND pins
Set RST and XTAL1 to GND
2. Set pin RST to “H”
Set pin P3.2 to “H”
3. Apply the appropriate combination of “H” or “L” logic
levels to pins P3.3, P3.4, P3.5, P3.7 to select one of the programming operations
shown in the PEROM Programming Modes table.
To Program and Verify the Array:
4. Apply data for Code byte at location 000H to P1.0 to P1.7.
5. Raise RST to 12V to enable programming.
6. Pulse P3.2 once to program a byte in the PEROM array or the lock bits. The byte-write cycle is self-timed and typically takes 1.2 ms.
7. To verify the programmed data, lower RST from 12V to logic “H” level and set pins P3.3 to P3.7 to the appropriate levels. Output data can be read at the port P1 pins.
8. To program a byte at the next address location, pulse XTAL1 pin once to advance the internal address counter. Apply new data to the port P1 pins.
9. Repeat steps 6 through 8, changing data and advancing the address counter for the entire 2K bytes array or until the end of the object file is reached.
10. Power-off sequence:
set XTAL1 to “L”
set RST to “L”
Turn VCC power off
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