83C754 Datasheet, PDF (21/26 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 4K/256 OTP/ROM, DAC, comparator, UART, reference

Philips Semiconductors
80C51 8-bit microcontroller family
4K/256 OTP/ROM, DAC, comparator, UART, reference
Preliminary specification
83C754/87C754
Programming and Verifying Security Bits
Security bits are programmed employing the same techniques used
to program the USER EPROM and KEY arrays using serial data
streams and logic levels on port pins indicated in Table 3. When
programming either security bit, it is not necessary to provide
address or data information to the 87C754 on ports 1 and 3.
Verification occurs in a similar manner using the RESET serial
stream shown in Table 3. Port 3 is not required to be driven and the
results of the verify operation will appear on ports 1.6 and 1.7.
Ports 1.7 contains the security bit 1 data and is a logical one if
programmed and a logical zero if erased. Likewise, P1.6 contains
the security bit 2 data and is a logical one if programmed and a
logical zero if erased.
Erasure Characteristics
Erasure of the EPROM begins to occur when the chip is exposed to
light with wavelengths shorter than approximately 4,000 angstroms.
Since sunlight and fluorescent lighting have wavelengths in this
range, exposure to these light sources over an extended time (about
1 week in sunlight, or 3 years in room level fluorescent lighting)
could cause inadvertent erasure. For this and secondary effects,
it is recommended that an opaque label be placed over the
window. For elevated temperature or environments where solvents
are being used, apply Kapton tape Flourless part number 2345–5 or
equivalent.
The recommended erasure procedure is exposure to ultraviolet light
(at 2537 angstroms) to an integrated dose of at least 15W-sec/cm².
Exposing the EPROM to an ultraviolet lamp of 12,000uW/cm² rating
for 20 to 39 minutes, at a distance of about 1 inch, should be
sufficient.
Erasure leaves the array in an all 1s state.
Table 3. Implementing Program/Verify Modes
OPERATION
SERIAL CODE
PGM
V_PP
Program user EPROM
Verify user EPROM
Program key EPROM
Verify key EPROM
Program security bit 1
Program security bit 2
Verify security bits
NOTE:
* Pulsed from V_IH to V_IL and returned to V_IH.
296H
–*
V_PP
296H
V_IH
V_IH
292H
–*
V_PP
292H
V_IH
V_IH
29AH
–*
V_PP
298H
–*
V_PP
29AH
V_IH
V_IH
1998 Apr 23
21