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AT89C55WD

1921B–MICRO–09/02

puts,and the nextcycle 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 out-

put 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 individ-

ual 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:

(000H) = 1EH indicates manufactured by Atmel

(100H) = 55H

(200H) = 06H indicates 89C55WD