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SN75970B2DGG Datasheet(PDF) 2 Page - Texas Instruments |
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SN75970B2DGG Datasheet(HTML) 2 Page - Texas Instruments |
2 / 23 page SN75970B SCSI DIFFERENTIAL CONVERTER-CONTROL SLLS323A – NOVEMBER 1999 – REVISED JANUARY 2000 2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 description (continued) The differential SCSI bus interface consists of bipolar bidirectional inputs and outputs that meet or exceed the requirements of EIA-485 and ISO 8482-1982/TIA TR30.2 referenced by the Ameri- can National Standard of Information Systems (ANSI) X3.131-1994 Small Computer System Interface-2 (SCSI-2) and SCSI-3 Fast-20 Parallel Interface (Fast-20) X3.277:1996. The SN75970B is characterized for operation over the temperature range of 0 °C to 70°C. The SN75970B consists of nine RS-485 differen- tial transceivers, nine TTL- or CMOS-level compatible transceivers, a state machine and control logic block, a 20-MHz crystal-controlled oscillator, a timer, a power-up/-down glitch protection circuit, and a thermal-shutdown protection circuit. The single-ended or controller interface is designated as the A side and the differential port is the B side. Since the device uses the SCSI control signals to decode the state of the bus and data flow direction, the terminal assignments must be matched to the corresponding signal on the SCSI bus. The signal name followed by a a minus sign (–) indicates an active-low signal while a plus sign (+) indicates an active-high signal. A reset function, which disables all outputs and clears internal latches, can be accomplished from two external inputs and two internally generated signals. RESET (Reset) and DSENS (differential sense) are available to external circuits for a bus reset or to disable all outputs should a single-ended cable be inadvertently connected to a differential connector. The power-up and thermal-shutdown are internally generated sig- nals that have the same effect when the supply voltage is below 3.5 V or the junction temperature exceeds approximately 175 °C. This data sheet contains descriptions of the SN75970B input and output signals followed by the electrical characteristics. The parameter measurement information is followed by the theory of operation, a state flow chart, and a typical circuit in the application information section. 53 52 BATN – BATN + 6 51 50 BACK – BACK + 8 38 37 BMSG – BMSG + 21 47 46 BC/D – BC/D + 11 36 35 BI/O – BI/O + 22 30 29 BRST + BRST – 27 H 32 31 BBSY + BBSY – 25 H 34 33 BSEL + BSEL – 23 H State Machine and Control Logic Oscillator H Thermal Shutdown Power-Up and Reset Logic 3 7 2 1 4 55 56 19 DRVBUS 20 SDB TIMEOUT AATN – AACK – AMSG – AC/D – AI/O – ARST – ABSY – ASEL – 49 48 BREQ – BREQ + 10 AREQ – 9 DSENS TEST RESET RSTFLTR CLK40 X1/CLK20 X2 logic diagram (positive logic) |
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