DS87000 Datasheet, PDF (8/10 Pages) Dallas Semiconductor – Microcontroller Programmer

DS87000
Read Button
The Read button causes all of the EPROM in the device to be read, and the contents stored in the
programmer's buffer memory. When the read process begins, the Busy light blinks to indicate that the
programmer is performing the requested operation. When the read operation is complete and no error has
occurred, the Complete light flashes. If an error occurs during the operation, the Error light flashes.
Since the Read operation destroys the existing contents of the programmer’s buffer, the button does not
activate the function immediately. The user is required to hold the button down for two seconds before the
operation begins. This eliminates the possibility of inadvertently initiating a read.
If none of the EPROM lock bits are set, and the device's encryption vector is blank (that is, all 1’s), then the
data output from the device during a read operation is precisely the data stored in its EPROM. However if a
value other than all 1’s is stored in the device’s encryption vector, the device will perform encryption on the
data as it is read out. This encryption process is the normal security measure offered by the encryption vector.
It should be noted that if a read is performed after the encryption vector is written, the programmer’s buffer
memory will be overwritten with encrypted data. This is typically not the desired result.
Lock bits also affect the read operation. If either of the upper two levels of lock (level 3 or 4) are set, the
device will output all 1’s when it is read. Therefore, the only way to distinguish between a blank device and
one that is locked is to try to program it. If a single location is programmed, and the program operation fails,
then the device is potentially locked.
Verify Button
When the Verify button is pressed, the Busy light begins flashing and the entire contents of the device's
EPROM memory are compared with the contents of the programmer's buffer memory. If the two contain the
same data, the Complete light flashes, but if there is a difference, the Error light flashes.
Since the verify operation performs a read of the device, the same comments on the encryption vector and
lock bits made in the Read Button section above also apply to the verify operation.
Blank Button
The blank button confirms that all of the device's EPROM memory is blank (all 1’s). The Busy light blinks to
indicate that the function is being performed and no error has been detected. If an error is detected (the
EPROM is not all 1’s), the process stops immediately and the Error light begins flashing. If the device is
blank, the Complete light will flash.
Note that the comments regarding the encryption vector and lock bits made in the above sections apply to the
Blank button as well.
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