AT89C55WD-33AU ATMEL [ATMEL Corporation], AT89C55WD-33AU Datasheet - Page 21

• Manufacturer Part Number: AT89C55WD-33AU
• Description: 8-bit Microcontroller with 20K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

21. Programming Interface
1921D–MICRO–6/08
Chip Erase Sequence: Before the AT89C55WD can be reprogrammed, a Chip Erase operation
needs to be performed. To erase the contents of the AT89C55WD, follow this sequence:
Data Polling: The AT89C55WD features Data Polling to indicate the end of a write cycle. During
a write cycle, an attempted read of the last byte written will result in the complement of the writ-
ten data on P0.7. Once the write cycle has been completed, true data is valid on all outputs, and
the next cycle may begin. Data Polling may begin any time after a write cycle has been initiated.
Ready/Busy: The progress of byte programming can also be monitored by the RDY/BSY output
signal. P3.0 is pulled low after ALE goes high during programming to indicate BUSY. P3.0 is
pulled high again when programming is done to indicate READY.
Program Verify: If lock bits LB1 and LB2 have not been programmed, the programmed code
data can be read back via the address and data lines for verification. The status of the individual
lock bits can be directly verified by reading them back.
Reading the Signature Bytes: The signature bytes are read by the same procedure as a nor-
mal verification of locations 000H, 100H, and 200H, except that P3.6 and P3.7 must be pulled to
a logic low. The values returned are as follows:
Every code byte in the Flash array can be programmed by using the appropriate combination of
control signals. The write operation cycle is self-timed and once initiated, will automatically time
itself to completion.
Most major worldwide programming vendors offer support for the Atmel AT89 microcontroller
series. Please contact your local programming vendor for the appropriate software revision.
1. Raise V
2. Pulse ALE/PROG once (duration of 200 - 500 ns).
3. Wait for 150 ms.
4. Power V
5. Pulse ALE/PROG once (duration of 200 - 500 ns).
6. Wait for 150 ms.
7. Power V
(000H) = 1EH indicates manufactured by Atmel
(100H) = 55H
(200H) = 06H indicates 89C55WD
CC
CC
CC
to 6.5V.
down and up.
down and up to 6.5V.
AT89C55WD
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