Rainbow Electronics AT89C55WD - Manual (Page 22)

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AT89C55WD
1921B–MICRO–09/02
puts, 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 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