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DP83924 Datasheet(PDF) 11 Page - National Semiconductor (TI) |
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DP83924 Datasheet(HTML) 11 Page - National Semiconductor (TI) |
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11 / 42 page  2.0 Interface Descriptions (Continued) 11 www.national.com If the standard 78 ohm transceiver cable is used, the receive differential input must be externally terminated with two 39 ohm resistors connected in series. In thin Ethernet applications, these resistors are optional. To prevent noise from falsely triggering the decoder, a squelch circuit at the input rejects signals with levels less than + 160mV. Signals with levels greater than + 300 mV are decoded. If the AUI interface is not used, the unused AUI inputs can be left floating or the +/- inputs could be shorted to each other and the unused AUI outputs should be left floating. 2.4.3 Oscillator Clock When using an oscillator, additional output drive may be necessary if the oscillator must also drive other compo- nents. The X1 pin is a simple TTL compatible input. See Figur e8. Table 7. MAC Interface Selection Parameter Mode 1 Mode 2 Mode 3 Mode 4 RXCs Active CRS + 5 clks CRS asserteda Continuous Continuous Edge of TXc that TXD is sampled Rising Rising Falling Falling Polarity of active TXE High High High High Edge of RXC that RXD is clocked Rising Rising Rising Falling Polarity of CRS asserted High High High High Level of RXD during CRS deassertion Low High Low Low Polarity of active COL High High High Low Polarity of active Loopback (LPBK) High High Low High How to select MAC interface mode b Using registers to select mode Global Control & Status Register (GCSR, addr 08H) bits D[8:6] 111 001 010 011 GCSR bit D[4] (select RXD_Idle level) 0 1 0 0 GCSR bit D[0] (select RXC modec) 11 00 Using strap options to select mode RXD[3:1] strap option (same as GCSR D[8:6]) 111 001 010 011 LINK[1] strap option (RXD idle level) 1 0 1 1 COL[4] strap option (RXC mode) 1 1 0 0 a. No extra clocks are added after CRS. (CRS + 0 clocks RXC mode) b. The mode can be selected by either strap options or writing to the registers. The default for both is NSC,TI. c. GCSR D[0] or COL[4] strap can’t be used to select CRS + 0 clocks RXC mode. This mode is selected by the GCSR bits D[8:6] or RXD[3:1] strap option. Table 8. Normal LED Mode LED Condition Status Indication Off Good Status On - Solid Error Statusa Fast Blink (400 ms) Link Lost Slow Blink (1600 ms) Bad Polarity a. Bit 7 of registers 00-03 can be set by the user /management entity based on any criteria they choose and will be used to turn on Error Status LED. Table 9. Enhanced LED Mode - Bit Decode FDX LinkCoded LED Status Comments 0 0 OFF Link Fail, Full Duplex 0 1 ON - Color A Good Link, Full Duplex 1 0 ON - Color B Good Link, Half Duplex 1 1 OFF Link Fail, Half Duplex |
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