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FDC37C78-HT Datasheet(PDF) 57 Page - Microchip Technology |
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FDC37C78-HT Datasheet(HTML) 57 Page - Microchip Technology |
57 / 82 page 57 LOCK In order to protect systems with long DMA latencies against older application software that can disable the FIFO the LOCK Command has been added. This command should only be used by the FDC routines, and application software should refrain from using it. If an application calls for the FIFO to be disabled then the CONFIGURE command should be used. The LOCK command defines whether the EFIFO, FIFOTHR, and PRETRK parameters of the CONFIGURE command can be RESET by the DOR and DSR registers. When the LOCK bit is set to logic "1" all subsequent "software RESETS by the DOR and DSR registers will not change the previously set parameters to their default values. All "hardware" RESET from the RESET pin will set the LOCK bit to logic "0" and return the EFIFO, FIFOTHR, and PRETRK to their default values. A status byte is returned immediately after issuing a a LOCK command. This byte reflects the value of the LOCK bit set by the command byte. ENHANCED DUMPREG The DUMPREG command is designed to support system run-time diagnostics and application software development and debug. To accommodate the LOCK command and the enhanced PERPENDICULAR MODE command the eighth byte of the DUMPREG command has been modified to contain the additional data from these two commands. COMPATIBILITY The FDC37C78 was designed with software compatibility in mind. It is a fully backwards- compatible solution with the older generation 765A/B disk controllers. The FDC also implements on-board registers for compatibility with PC/AT and PC/XT floppy disk controller subsystems. After a hardware reset of the FDC, all registers, functions and enhancements default to a PC/AT compatible operating mode. |
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