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83C752 Datasheet(PDF) 17 Page - NXP Semiconductors |
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83C752 Datasheet(HTML) 17 Page - NXP Semiconductors |
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17 / 24 page  Philips Semiconductors Product specification 83C752/87C752 80C51 8-bit microcontroller family 2K/64 OTP/ROM, 5 channel 8 bit A/D, I2C, PWM, low pin count 1998 May 01 17 A high voltage VPP level is then applied to the VPP input (P0.2). (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 repeated until a total of 25 programming pulses have occurred. At the conclusion of the last pulse, the PGM/ signal should remain high. The VPP signal may now be driven to the VOH level, placing the 87C752 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 VPP pin to the VPP voltage level, providing the byte to be programmed to Port1 and issuing the 26 programming pulses on the PGM/ pin, bringing VPP back down to the VC level and verifying the byte. Programming Modes The 87C752 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 4. Encryption Key Table The 87C752 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 still be performed. (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. 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 4. When programming either security bit, it is not necessary to provide address or data information to the 87C752 on ports 1 and 3. Verification occurs in a similar manner using the RESET serial stream shown in Table 4. 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 not programmed. Likewise, P1.6 contains the security bit 2 data and is a logical one if programmed and a logical zero if not programmed. Table 4. Implementing Program/Verify Modes OPERATION SERIAL CODE P0.1 (PGM/) P0.2 (VPP) Program user EPROM 296H –* VPP Verify user EPROM 296H VIH VIH Program key EPROM 292H –* VPP Verify key EPROM 292H VIH VIH Program security bit 1 29AH –* VPP Program security bit 2 298H –* VPP Verify security bits 29AH VIH VIH NOTE: * Pulsed from VIH to VIL and returned to VIH. |
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