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83C749 Datasheet(PDF) 15 Page - NXP Semiconductors |
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83C749 Datasheet(HTML) 15 Page - NXP Semiconductors |
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15 / 22 page  Philips Semiconductors Preliminary specification 83C749/87C749 80C51 8-bit microcontroller family 2K/64 OTP/ROM, 5 channel 8-bit A/D, PWM, low pin count 1998 Apr 23 15 PROGRAMMING CONSIDERATIONS EPROM Characteristics The 87C749 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 87C749 in the programming mode. Figure 7 shows a block diagram of the programming configuration for the 87C749. Port pin P0.2 is used as the programming voltage supply input (VPP signal). Port pin P0.1 is used as the program (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 87C749 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 8 and 9 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 (VPP) will be at VOH as a result of the 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 (VIH). The RESET pin may now be used as the serial data input for the data stream which places the 87C749 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 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 87C749 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 87C749 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 87C749 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. |
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