P87C750EBAA PHILIPS [NXP Semiconductors], P87C750EBAA Datasheet - Page 9

• Manufacturer Part Number: P87C750EBAA
• Description: 80C51 8-bit microcontroller family 1K/64 OTP ROM, low pin count
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
87C750 PROGRAMMING CONSIDERATIONS
EPROM Characteristics
The 87C750 is programmed by using a modified Quick-Pulse
Programming algorithm similar to that used for devices such as the
87C451 and 87C51. It differs from these devices in that a serial data
stream is used to place the 87C750 in the programming mode.
Figure 4 shows a block diagram of the programming configuration
for the 87C750. Port pin P0.2 is used as the programming voltage
supply input (V
(PGM/) signal. This pin is used for the 25 programming pulses.
Port 3 is used as the address input for the byte to be programmed
and accepts both the high and low components of the eleven bit
address. Multiplexing of these address components is performed
using the ASEL input. The user should drive the ASEL input high
and then drive port 3 with the high order bits of the address. ASEL
should remain high for at least 13 clock cycles. ASEL may then be
driven low which latches the high order bits of the address internally.
the high address should remain on port 3 for at least two clock
cycles after ASEL is driven low. Port 3 may then be driven with the
low byte of the address. The low address will be internally stable 13
clock cycles later. The address will remain stable provided that the
low byte placed on port 3 is held stable and ASEL is kept low. Note:
ASEL needs to be pulsed high only to change the high byte of the
address.
Port 1 is used as a bidirectional data bus during programming and
verify operations. During programming mode, it accepts the byte to
be programmed. During verify mode, it provides the contents of the
EPROM location specified by the address which has been supplied
to Port 3.
The XTAL1 pin is the oscillator input and receives the master system
clock. This clock should be between 1.2 and 6MHz.
The RESET pin is used to accept the serial data stream that places
the 87C750 into various programming modes. This pattern consists
of a 10-bit code with the LSB sent first. Each bit is synchronized to
the clock input, X1.
Programming Operation
Figures 5 and 6 show the timing diagrams for the program/verify
cycle. RESET should initially be held high for at least two machine
cycles. P0.1 (PGM/) and P0.2 (V
RESET operation. At this point, these pins function as normal
quasi-bidirectional I/O ports and the programming equipment may
pull these lines low. However, prior to sending the 10-bit code on the
RESET pin, the programming equipment should drive these pins
high (V
for the data stream which places the 87C750 in the programming
mode. Data bits are sampled during the clock high time and thus
should only change during the time that the clock is low. Following
transmission of the last data bit, the RESET pin should be held low.
Next the address information for the location to be programmed is
placed on port 3 and ASEL is used to perform the address
multiplexing, as previously described. At this time, port 1 functions
as an output.
A high voltage V
(This sets Port 1 as an input port). The data to be programmed into
the EPROM array is then placed on Port 1. This is followed by a
series of programming pulses applied to the PGM/ pin (P0.1). These
pulses are created by driving P0.1 low and then high. This pulse is
1998 May 01
80C51 8-bit microcontroller family
1K/64 OTP/ROM, low pin count
IH
). The RESET pin may now be used as the serial data input
PP
PP
signal). Port pin P0.1 is used as the program
level is then applied to the V
PP
) will be at V
OH
PP
as a result of the
input (P0.2).
9
repeated until a total of 25 programming pulses have occurred. At
the conclusion of the last pulse, the PGM/ signal should remain high.
The V
87C750 in the verify mode. (Port 1 is now used as an output port).
After four machine cycles (48 clock periods), the contents of the
addressed location in the EPROM array will appear on Port 1.
The next programming cycle may now be initiated by placing the
address information at the inputs of the multiplexed buffers, driving
the V
programmed to Port1 and issuing the 26 programming pulses on the
PGM/ pin, bringing V
byte.
Programming Modes
The 87C750 has four programming features incorporated within its
EPROM array. These include the USER EPROM for storage of the
application’s code, a 16-byte encryption key array and two security
bits. Programming and verification of these four elements are
selected by a combination of the serial data stream applied to the
RESET pin and the voltage levels applied to port pins P0.1 and
P0.2. The various combinations are shown in Table 3.
Encryption Key Table
The 87C750 includes a 16-byte EPROM array that is programmable
by the end user. The contents of this array can then be used to
encrypt the program memory contents during a program memory
verify operation. When a program memory verify operation is
performed, the contents of the program memory location is
XNOR’ed with one of the bytes in the 16-byte encryption table. The
resulting data pattern is then provided to port 1 as the verify data.
The encryption mechanism can be disable, in essence, by leaving
the bytes in the encryption table in their erased state (FFH) since
the XNOR product of a bit with a logical one will result in the original
bit. The encryption bytes are mapped with the code memory in
16-byte groups. the first byte in code memory will be encrypted with
the first byte in the encryption table; the second byte in code
memory will be encrypted with the second byte in the encryption
table and so forth up to and including the 16the byte. The encryption
repeats in 16-byte groups; the 17th byte in the code memory will be
encrypted with the first byte in the encryption table, and so forth.
Security Bits
Two security bits, security bit 1 and security bit 2, are provided to
limit access to the USER EPROM and encryption key arrays.
Security bit 1 is the program inhibit bit, and once programmed
performs the following functions:
1. Additional programming of the USER EPROM is inhibited.
2. Additional programming of the encryption key is inhibited.
3. Verification of the encryption key is inhibited.
4. Verification of the USER EPROM and the security bit levels may
(If the encryption key array is being used, this security bit should be
programmed by the user to prevent unauthorized parties from
reprogramming the encryption key to all logical zero bits. Such
programming would provide data during a verify cycle that is the
logical complement of the USER EPROM contents).
Security bit 2, the verify inhibit bit, prevents verification of both the
USER EPROM array and the encryption key arrays. The security bit
levels may still be verified.
still be performed.
PP
PP
pin to the V
signal may now be driven to the V
PP
PP
voltage level, providing the byte to be
back down to the V
83C750/87C750
OH
C
level and verifying the
level, placing the
Product specification