參數(shù)資料
型號： LXT970A
廠商： Intel Corp.
英文描述： Dual-Speed Fast Ethernet Transceiver
中文描述： 雙速度快速以太網(wǎng)收發(fā)器
文件頁數(shù)： 38/74頁
文件大?。?/td> 1061K
代理商： LXT970A
LXT970A
—
Dual-Speed Fast Ethernet Transceiver
38
Datasheet
2.8.1.5
SQE (10T Only)
When the SQE (heartbeat) function is enabled, the LXT970A asserts its COL output for 5-15 BT
after each packet. By default, the SQE function is disabled on the LXT970A. To enable SQE, set
bit 19.10 = 1. See
Figure 30 on page 59
for SQE timing parameters.
2.8.1.6
Jabber (10T Only)
If the MAC transmission exceeds the jabber timer, the LXT970A disables the transmit and
loopback functions and asserts the COL pin. The LXT970A automatically exits jabber mode after
250-750 ms. This function can be disabled by setting bit 19.9 = 1. See
Figure 31 on page 59
for
Jabber timing parameters.
2.8.2
PMA Layer
The Physical Medium Attachment (PMA) layer provides link and carrier status functions.
2.8.2.1
100TX Link Options
The LXT970A uses standard symbol error rate criteria to establish a link and has two options for
100TX and 100FX applications to break down a link:
Standard (symbol error rate).
Enhanced (scrambler lock).
Standard link criteria (17.2 = 0 default), takes down the link when the Bit Error Rate (BER)
exceeds the allowable standards. If the link goes down and auto-negotiation is enabled, the device
automatically restarts the auto-negotiation process. Otherwise the device continues to monitor the
line for a valid link. With this option both link up and link loss are based on symbol error rate.
Enhanced link-loss criteria (17.2 = 1) works independent of symbol error rate. The loss of
scrambler lock for more than 1 - 2 msec brings the link down. Enhanced link-loss criteria is not
available in 5B mode.
2.8.2.2
10T Link Test
For 10T operation, link is detected via Normal Link Pulses (NLPs). In 10T mode, the LXT970A
always transmits link pulses. If the Link Test Function is enabled, it monitors the connection for
link pulses. Once it detects 2 to 7 link pulses, data transmission will be enabled and remains
enabled as long as the link pulses or data transmission continues. Link failure occurs if Link Test is
enabled and link pulses are no longer received. When this condition occurs, the LXT970A returns
to the auto-negotiation phase if auto-negotiation is enabled. If the Link Test function is disabled,
the LXT970A transmits to the connection regardless of detected link pulses. The Link Test
function can be disabled by setting bit 19.8 = 1 or by setting MF0 to disable auto-negotiation and
setting CFG1 input High.
2.8.2.3
Carrier Sense (CRS)
For 100TX and 100FX links, a start-of-stream delimiter or /J/K symbol pair causes assertion of
carrier sense (CRS). An end-of-stream delimiter, or /T/R symbol pair causes deassertion of CRS.
The PMA layer also de-asserts CRS if IDLE symbols are received without /T/R, however, in this
case RX_ER asserts for one clock cycle when CRS is de-asserted.
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