at89c55-12qi ATMEL Corporation, at89c55-12qi Datasheet - Page 14

• Manufacturer Part Number: at89c55-12qi
• Description: 8-bit Microcontroller With Bytes Flash
• Manufacturer: ATMEL Corporation

Programming the Flash (Continued)
Data Polling: The AT89C55 features Data Polling to indi-
cate the end of a write cycle. During a write cycle, an at-
tempted read of the last byte written will result in the com-
plement of the written data on PO.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:
also be monitored by the RDY/BSY output signal. P3.4 is
pulled low after ALE goes high during programming to in-
dicate BUSY. P3.4 is pulled high again when program-
ming 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
lock bits cannot be verified directly. Verification of the lock
bits is achieved by observing that their features are en-
abled.
Figure 9. Programming the Flash Memory
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memory address line A14 (P2.6)
Programming address line A14 (P3.0) is not the same as the external
The progress of byte programming can
AT89C55
Chip Erase: The entire Flash array is erased electrically
by using the proper combination of control signals and by
holding ALE/PROG low for 10 ms. The code array is writ-
ten with all 1s. The chip erase operation must be executed
before the code memory can be reprogrammed.
Reading the Signature Bytes: The signature bytes are
read by the same procedure as a normal verification of
locations 030H, 031H, and 032H, except that P3.6 and
P3.7 must be pulled to a logic low. The values returned are
as follows.
Programming Interface
Every code byte in the Flash array can be written, and the
entire array can be erased, by using the appropriate com-
bination of control signals. The write operation cycle is
self-timed and once initiated, will automatically time itself
to completion.
All major programming vendors offer worldwide support
for the Atmel microcontroller series. Please contact your
local programming vendor for the appropriate software re-
vision.
Figure 10. Verifying the Flash Memory
(030H) = 1EH indicates manufactured by Atmel
(031H) = 55H indicates 89C55
(032H) = FFH indicates 12V programming
(032H) = 05H indicates 5V programming