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PC8477BVF-1 Datasheet(PDF) 50 Page - National Semiconductor (TI) |
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PC8477BVF-1 Datasheet(HTML) 50 Page - National Semiconductor (TI) |
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50 / 54 page  70 Reference Section (Continued) 73 PC8477B INTERFACE IN A PC-AT The PC8477B interface to the PC-AT bus is simple and re- quires only an external address decoder All the microproc- essor inputs and outputs of the PC8477B can be connected directly to the peripheral bus due to the 12 mA sink capabili- ty Figure 7-1 shows the interface with the floppy drive header and the signal connections to the AT bus The de- sign will support 12 Meg 144 Meg and 288 Meg drives Support for the 288 Meg perpendicular drives is accom- plished with the additional density encoding signal (DRATE0) on floppy header pin 6 This interface solution will support perpendicular drives with the encoding scheme list- ed in Table 7-2 below TABLE 7-2 Density Encoding Media Data Rate HD ED 1 Meg 250 kbs 0 0 2 Meg 500 kbs 1 0 4 Meg 1 Mbs X 1 The HD signal is floppy header pin 2 and the ED signal is header pin 6 This standard scheme is supported by a num- ber of perpendicular drive manufacturers Some new per- pendicular drives are using an auto media sense for density selection These drives will not require either the HD or ED signals Here the data rate is determined optically by the drive due to the hole in the disk The only use of the 16L8 PAL is address decoding for the proper floppy address range The primary range is 3F0 – 3F7 while the secondary address range is 370 – 377 Selection between can be accomplished with a jumper if needed The address lines A9 – A3 and AEN are input to the PAL from the peripheral bus The following equation can be used for the primary range CS e (AEN A9 A8 A7 A6 A5 A4 A3) In this design we have used 1 kX pull-up resistors on the floppy drive interface If the intended design is to be used with external drives or long cabling or if 525 disk drives are to be supported 150 kX pull-ups should be considered TLF11332 – 24 FIGURE 7-1 8477B in PC-AT System 50 |
Similar Part No. - PC8477BVF-1 |
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Similar Description - PC8477BVF-1 |
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