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PIC24FJ64GA 数据表(PDF) 35 Page - Microchip Technology |
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PIC24FJ64GA 数据表(HTML) 35 Page - Microchip Technology |
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35 / 52 page  © 2008 Microchip Technology Inc. DS39768D-page 35 PIC24FJXXXGA0XX FIGURE 5-3: PROGRAMMING EXECUTIVE – PROGRAMMER COMMUNICATION PROTOCOL 5.2 Programming Executive Commands The programming executive command set is shown in Table 5-1. This table contains the opcode, mnemonic, length, time-out and description for each command. Functional details on each command are provided in Section 5.2.4 “Command Descriptions”. 5.2.1 COMMAND FORMAT All programming executive commands have a general format consisting of a 16-bit header and any required data for the command (see Figure 5-4). The 16-bit header consists of a 4-bit opcode field, which is used to identify the command, followed by a 12-bit command length field. FIGURE 5-4: COMMAND FORMAT The command opcode must match one of those in the command set. Any command that is received which does not match the list in Table 5-1 will return a “NACK” response (see Section 5.3.1.1 “Opcode Field”). The command length is represented in 16-bit words since the SPI operates in 16-bit mode. The program- ming executive uses the command length field to determine the number of words to read from the SPI port. If the value of this field is incorrect, the command will not be properly received by the programming executive. 5.2.2 PACKED DATA FORMAT When 24-bit instruction words are transferred across the 16-bit SPI interface, they are packed to conserve space using the format shown in Figure 5-5. This format minimizes traffic over the SPI and provides the programming executive with data that is properly aligned for performing table write operations. FIGURE 5-5: PACKED INSTRUCTION WORD FORMAT 5.2.3 PROGRAMMING EXECUTIVE ERROR HANDLING The programming executive will “NACK” all unsupported commands. Additionally, due to the memory constraints of the programming executive, no checking is performed on the data contained in the programmer command. It is the responsibility of the programmer to command the programming executive with valid command arguments or the programming operation may fail. Additional information on error handling is provided in Section 5.3.1.3 “QE_Code Field”. 1 2 15 16 1 2 15 16 PGCx PGDx PGCx = Input PGCx = Input (Idle) Host Transmits Last Command Word PGDx = Input PGDx = Output P8 12 15 16 MSB X X X LSB MSB X X X LSB MSB X X X LSB 1 0 P20 PGCx = Input PGDx = Output P9 Programming Executive Processes Command Host Clocks Out Response P21 15 12 11 0 Opcode Length Command Data First Word (if required) • • Command Data Last Word (if required) Note: When the number of instruction words transferred is odd, MSB2 is zero and LSW2 can not be transmitted. 15 8 7 0 LSW1 MSB2 MSB1 LSW2 LSWx: Least Significant 16 bits of instruction word MSBx: Most Significant Bytes of instruction word |
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