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PIC24FJ64GA 数据表(PDF) 15 Page - Microchip Technology |
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PIC24FJ64GA 数据表(HTML) 15 Page - Microchip Technology |
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15 / 52 page ![]() © 2008 Microchip Technology Inc. DS39768D-page 15 PIC24FJXXXGA0XX 3.3 Entering ICSP Mode As shown in Figure 3-4, entering ICSP Program/Verify mode requires three steps: 1. MCLR is briefly driven high, then low. 2. A 32-bit key sequence is clocked into PGDx. 3. MCLR is then driven high within a specified period of time and held. The programming voltage applied to MCLR is VIH, which is essentially VDD in the case of PIC24FJXXXGA0XX devices. There is no minimum time requirement for holding at VIH. After VIH is removed, an interval of at least P18 must elapse before presenting the key sequence on PGDx. The key sequence is a specific 32-bit pattern: ‘0100 1101 0100 0011 0100 1000 0101 0001’ (more easily remembered as 4D434851h in hexa- decimal). The device will enter Program/Verify mode only if the sequence is valid. The Most Significant bit (MSb) of the most significant nibble must be shifted in first. Once the key sequence is complete, VIH must be applied to MCLR and held at that level for as long as Program/Verify mode is to be maintained. An interval of at least time, P19 and P7, must elapse before present- ing data on PGDx. Signals appearing on PGCx before P7 has elapsed will not be interpreted as valid. On successful entry, the program memory can be accessed and programmed in serial fashion. While in ICSP mode, all unused I/Os are placed in the high-impedance state. FIGURE 3-4: ENTERING ICSP™ MODE MCLR PGDx PGCx VDD P6 P14 b31 b30 b29 b28 b27 b2 b1 b0 b3 ... Program/Verify Entry Code = 4D434851h P1A P1B P18 P19 010 0 0 0 P7 VIH VIH 1 0 1 |
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