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Eprom is the place where store the heximal of NXP P87C451 Chip, so it is necessary to have a better understand about the eprom characteristic before execute the NXP P87C451 Chip Heximal Duplication.

All these devices can be programmed by using a modified Improved Quick-Pulse Programming algorithm. It differs from older methods in the value used for VPP (programming supply voltage) and in the width and number of the ALE/PROG pulses.
The family contains two signature bytes that can be read and used by an EPROM programming system to identify the device. The signature bytes identify the device as being manufactured by Philips.
Below Table shows the logic levels for reading the signature byte, and for programming the program memory,

EPROM Programming Modes

the encryption table, and the security bits. The circuit configuration and waveforms for quick-pulse programming are shown in below Figures.

NXP P87C451 Chip Heximal Duplication

The setup for microcontroller quick-pulse programming is shown in Figure 41. Note that the device is running with a 4 to 6MHz oscillator before NXP P87C451 Chip Heximal Duplication. The reason the oscillator needs to be running is that the device is executing internal address and program data transfers.
The address of the EPROM location to be programmed is applied to ports 1 and 2, as shown in Figure 41. The code byte to be programmed into that location is applied to port 0. RST, PSEN and pins of ports 2 and 3 specified in Table 9 are held at the ‘Program Code Data’ levels indicated in Table 9. The ALE/PROG is pulsed low 5 times as shown in Figure 42.
To program the encryption table, repeat the 5 pulse programming sequence for addresses 0 through 1FH, using the ‘Pgm Encryption Table’ levels. Do not forget that after the encryption table is programmed, verification cycles will produce only encrypted data.