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PC87309VLJ 数据表(PDF) 41 Page - National Semiconductor (TI) |
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PC87309VLJ 数据表(HTML) 41 Page - National Semiconductor (TI) |
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41 / 192 page  The Floppy Disk Controller (FDC) (Logical Device 0) 41 www.national.com 3.3.4 Tape Drive Register (TDR) The TDR register is a read/write register that acts as the Floppy Disk Controller’s (FDC) drive type register. AT Compatible TDR Mode In this mode, the TDR assigns a drive number to the tape drive support mode of the data separator. All other logical drives can be assigned as floppy drive support. Bits 7-2 are in TRI-STATE during read operations. Enhanced TDR Mode In this mode, all the bits of the TDR define operations with Enhanced floppy disk drives. TABLE 3-4. TDR Bit Utilization and Reset Values in Different Drive Modes Bits 1,0 - Tape Drive Select 1,0 These bits assign a logical drive number to a tape drive. Drive 0 is not available as a tape drive and is reserved as the floppy disk boot drive. 00: No drive selected. 01: Drive 1 selected. 10: Drive 2 selected. 11: Drive 3 selected. Bits 3,2 - Logical Drive Control (Enhanced TDR Mode Only) These read/write bits control logical drive exchange be- tween drives 0 and 2, only. They enable software to exchange the physical floppy disk drive and motor control signals assigned to pins. Drive 3 is never exchanged for drive 2. When four drives are configured, i.e., bit 7 of SuperI/O FDC Configuration register at index F0h is 1, logical drives are not exchanged. 00: No logical drive exchange. 01: Disk drive and motor control signal assignment to pins exchanged between logical drives 0 and 1. 10: Disk drive and motor control signal assignment to pins exchanged between logical drives 0 and 2. 11: Reserved. Unpredictable results when configured. Bits 5,4 - Drive ID1,0 Information If the value of bits 1,0 of the Digital Output Register (DOR) are 00, these bits reflect the ID of drive 0, i.e., the value of bits 1,0, respectively, of the Drive ID register at index F1h. See “Bits 1,0 - Drive 0 ID” on page 30. If the value of bits 1,0 of the Digital Output Register (DOR) are 01, these bits reflect the ID of drive 1, i.e., the value of bits 3,2, respectively, of the Drive ID register at index F1h. See “Bits 3,2 - Drive 1 ID” on page 30. Bits 7,6 - Reserved. These bits are reserved and are read as 11b. 76543210 Reset Required 0 0 1 Tape Drive Register (TDR) Offset 03h Tape Drive Select 1,0 AT Compatible TDR Mode TRI-STATE During Read Operations Not Used 76543210 Reset Required 0 0 1 Tape Drive Register (TDR) Offset 03h Reserved Reserved Tape Drive Select 1,0 Logical Drive Exchange Enhanced TDR Mode Drive ID1 Information Drive ID0 Information TDR Mode Bit 6 of SuperI/O FDC Configuration Register Bits of TDR Drive ID1 Drive ID0 Logical Drive Exchange Drive Select 5432 1 0 PC-AT Compatible 0 Not used. Floated in TRI-STATE during read operations. 00 Enhanced 1 1 1 0 0 0 0 |
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